diff options
| -rw-r--r-- | drivers/tty/serial/8250/8250_core.c | 6 | ||||
| -rw-r--r-- | drivers/tty/serial/amba-pl011.c | 2 | ||||
| -rw-r--r-- | drivers/tty/serial/serial_core.c | 16 | ||||
| -rw-r--r-- | drivers/tty/tty_io.c | 2 | ||||
| -rw-r--r-- | fs/proc/consoles.c | 7 | ||||
| -rw-r--r-- | include/linux/console.h | 158 | ||||
| -rw-r--r-- | include/linux/printk.h | 33 | ||||
| -rw-r--r-- | include/linux/serial_core.h | 117 | ||||
| -rw-r--r-- | kernel/locking/lockdep.c | 83 | ||||
| -rw-r--r-- | kernel/panic.c | 9 | ||||
| -rw-r--r-- | kernel/printk/internal.h | 207 | ||||
| -rw-r--r-- | kernel/printk/nbcon.c | 934 | ||||
| -rw-r--r-- | kernel/printk/printk.c | 712 | ||||
| -rw-r--r-- | kernel/printk/printk_ringbuffer.h | 7 | ||||
| -rw-r--r-- | kernel/printk/printk_safe.c | 25 | ||||
| -rw-r--r-- | kernel/rcu/tree_exp.h | 7 | ||||
| -rw-r--r-- | kernel/rcu/tree_stall.h | 9 |
17 files changed, 2123 insertions, 211 deletions
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 29e4b83e0376..5f9f06911795 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -423,11 +423,11 @@ static int univ8250_console_setup(struct console *co, char *options) port = &serial8250_ports[co->index].port; /* link port to console */ - port->cons = co; + uart_port_set_cons(port, co); retval = serial8250_console_setup(port, options, false); if (retval != 0) - port->cons = NULL; + uart_port_set_cons(port, NULL); return retval; } @@ -485,7 +485,7 @@ static int univ8250_console_match(struct console *co, char *name, int idx, continue; co->index = i; - port->cons = co; + uart_port_set_cons(port, co); return serial8250_console_setup(port, options, true); } diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 8b1644f5411e..7d0134ecd82f 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -2480,7 +2480,7 @@ static int pl011_console_match(struct console *co, char *name, int idx, continue; co->index = i; - port->cons = co; + uart_port_set_cons(port, co); return pl011_console_setup(co, options); } diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 5bea3af46abc..1e3e28e364df 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -3176,8 +3176,15 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u state->uart_port = uport; uport->state = state; + /* + * If this port is in use as a console then the spinlock is already + * initialised. + */ + if (!uart_console_registered(uport)) + uart_port_spin_lock_init(uport); + state->pm_state = UART_PM_STATE_UNDEFINED; - uport->cons = drv->cons; + uart_port_set_cons(uport, drv->cons); uport->minor = drv->tty_driver->minor_start + uport->line; uport->name = kasprintf(GFP_KERNEL, "%s%d", drv->dev_name, drv->tty_driver->name_base + uport->line); @@ -3186,13 +3193,6 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u goto out; } - /* - * If this port is in use as a console then the spinlock is already - * initialised. - */ - if (!uart_console_registered(uport)) - uart_port_spin_lock_init(uport); - if (uport->cons && uport->dev) of_console_check(uport->dev->of_node, uport->cons->name, uport->line); diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 7ae0c8934f42..abc2708d4ac5 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -3573,7 +3573,7 @@ static ssize_t show_cons_active(struct device *dev, for_each_console(c) { if (!c->device) continue; - if (!c->write) + if (!(c->flags & CON_NBCON) && !c->write) continue; if ((c->flags & CON_ENABLED) == 0) continue; diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c index e0758fe7936d..b7cab1ad990d 100644 --- a/fs/proc/consoles.c +++ b/fs/proc/consoles.c @@ -21,6 +21,7 @@ static int show_console_dev(struct seq_file *m, void *v) { CON_ENABLED, 'E' }, { CON_CONSDEV, 'C' }, { CON_BOOT, 'B' }, + { CON_NBCON, 'N' }, { CON_PRINTBUFFER, 'p' }, { CON_BRL, 'b' }, { CON_ANYTIME, 'a' }, @@ -58,8 +59,8 @@ static int show_console_dev(struct seq_file *m, void *v) seq_printf(m, "%s%d", con->name, con->index); seq_pad(m, ' '); seq_printf(m, "%c%c%c (%s)", con->read ? 'R' : '-', - con->write ? 'W' : '-', con->unblank ? 'U' : '-', - flags); + ((con->flags & CON_NBCON) || con->write) ? 'W' : '-', + con->unblank ? 'U' : '-', flags); if (dev) seq_printf(m, " %4d:%d", MAJOR(dev), MINOR(dev)); @@ -68,6 +69,7 @@ static int show_console_dev(struct seq_file *m, void *v) } static void *c_start(struct seq_file *m, loff_t *pos) + __acquires(&console_mutex) { struct console *con; loff_t off = 0; @@ -94,6 +96,7 @@ static void *c_next(struct seq_file *m, void *v, loff_t *pos) } static void c_stop(struct seq_file *m, void *v) + __releases(&console_mutex) { console_list_unlock(); } diff --git a/include/linux/console.h b/include/linux/console.h index 31a8f5b85f5d..eba367bf605d 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -16,7 +16,9 @@ #include <linux/atomic.h> #include <linux/bits.h> +#include <linux/irq_work.h> #include <linux/rculist.h> +#include <linux/rcuwait.h> #include <linux/types.h> #include <linux/vesa.h> @@ -303,7 +305,7 @@ struct nbcon_write_context { /** * struct console - The console descriptor structure * @name: The name of the console driver - * @write: Write callback to output messages (Optional) + * @write: Legacy write callback to output messages (Optional) * @read: Read callback for console input (Optional) * @device: The underlying TTY device driver (Optional) * @unblank: Callback to unblank the console (Optional) @@ -320,10 +322,14 @@ struct nbcon_write_context { * @data: Driver private data * @node: hlist node for the console list * - * @write_atomic: Write callback for atomic context * @nbcon_state: State for nbcon consoles * @nbcon_seq: Sequence number of the next record for nbcon to print + * @nbcon_device_ctxt: Context available for non-printing operations + * @nbcon_prev_seq: Seq num the previous nbcon owner was assigned to print * @pbufs: Pointer to nbcon private buffer + * @kthread: Printer kthread for this console + * @rcuwait: RCU-safe wait object for @kthread waking + * @irq_work: Defer @kthread waking to IRQ work context */ struct console { char name[16]; @@ -345,11 +351,121 @@ struct console { struct hlist_node node; /* nbcon console specific members */ - bool (*write_atomic)(struct console *con, - struct nbcon_write_context *wctxt); + + /** + * @write_atomic: + * + * NBCON callback to write out text in any context. (Optional) + * + * This callback is called with the console already acquired. However, + * a higher priority context is allowed to take it over by default. + * + * The callback must call nbcon_enter_unsafe() and nbcon_exit_unsafe() + * around any code where the takeover is not safe, for example, when + * manipulating the serial port registers. + * + * nbcon_enter_unsafe() will fail if the context has lost the console + * ownership in the meantime. In this case, the callback is no longer + * allowed to go forward. It must back out immediately and carefully. + * The buffer content is also no longer trusted since it no longer + * belongs to the context. + * + * The callback should allow the takeover whenever it is safe. It + * increases the chance to see messages when the system is in trouble. + * If the driver must reacquire ownership in order to finalize or + * revert hardware changes, nbcon_reacquire_nobuf() can be used. + * However, on reacquire the buffer content is no longer available. A + * reacquire cannot be used to resume printing. + * + * The callback can be called from any context (including NMI). + * Therefore it must avoid usage of any locking and instead rely + * on the console ownership for synchronization. + */ + void (*write_atomic)(struct console *con, struct nbcon_write_context *wctxt); + + /** + * @write_thread: + * + * NBCON callback to write out text in task context. + * + * This callback must be called only in task context with both + * device_lock() and the nbcon console acquired with + * NBCON_PRIO_NORMAL. + * + * The same rules for console ownership verification and unsafe + * sections handling applies as with write_atomic(). + * + * The console ownership handling is necessary for synchronization + * against write_atomic() which is synchronized only via the context. + * + * The device_lock() provides the primary serialization for operations + * on the device. It might be as relaxed (mutex)[*] or as tight + * (disabled preemption and interrupts) as needed. It allows + * the kthread to operate in the least restrictive mode[**]. + * + * [*] Standalone nbcon_context_try_acquire() is not safe with + * the preemption enabled, see nbcon_owner_matches(). But it + * can be safe when always called in the preemptive context + * under the device_lock(). + * + * [**] The device_lock() makes sure that nbcon_context_try_acquire() + * would never need to spin which is important especially with + * PREEMPT_RT. + */ + void (*write_thread)(struct console *con, struct nbcon_write_context *wctxt); + + /** + * @device_lock: + * + * NBCON callback to begin synchronization with driver code. + * + * Console drivers typically must deal with access to the hardware + * via user input/output (such as an interactive login shell) and + * output of kernel messages via printk() calls. This callback is + * called by the printk-subsystem whenever it needs to synchronize + * with hardware access by the driver. It should be implemented to + * use whatever synchronization mechanism the driver is using for + * itself (for example, the port lock for uart serial consoles). + * + * The callback is always called from task context. It may use any + * synchronization method required by the driver. + * + * IMPORTANT: The callback MUST disable migration. The console driver + * may be using a synchronization mechanism that already takes + * care of this (such as spinlocks). Otherwise this function must + * explicitly call migrate_disable(). + * + * The flags argument is provided as a convenience to the driver. It + * will be passed again to device_unlock(). It can be ignored if the + * driver does not need it. + */ + void (*device_lock)(struct console *con, unsigned long *flags); + + /** + * @device_unlock: + * + * NBCON callback to finish synchronization with driver code. + * + * It is the counterpart to device_lock(). + * + * This callback is always called from task context. It must + * appropriately re-enable migration (depending on how device_lock() + * disabled migration). + * + * The flags argument is the value of the same variable that was + * passed to device_lock(). + */ + void (*device_unlock)(struct console *con, unsigned long flags); + atomic_t __private nbcon_state; atomic_long_t __private nbcon_seq; + struct nbcon_context __private nbcon_device_ctxt; + atomic_long_t __private nbcon_prev_seq; + struct printk_buffers *pbufs; + struct task_struct *kthread; + struct rcuwait rcuwait; + struct irq_work irq_work; }; #ifdef CONFIG_LOCKDEP @@ -378,28 +494,34 @@ extern void console_list_unlock(void) __releases(console_mutex); extern struct hlist_head console_list; /** - * console_srcu_read_flags - Locklessly read the console flags + * console_srcu_read_flags - Locklessly read flags of a possibly registered + * console * @con: struct console pointer of console to read flags from * - * This function provides the necessary READ_ONCE() and data_race() - * notation for locklessly reading the console flags. The READ_ONCE() - * in this function matches the WRITE_ONCE() when @flags are modified - * for registered consoles with console_srcu_write_flags(). + * Locklessly reading @con->flags provides a consistent read value because + * there is at most one CPU modifying @con->flags and that CPU is using only + * read-modify-write operations to do so. + * + * Requires console_srcu_read_lock to be held, which implies that @con might + * be a registered console. The purpose of holding console_srcu_read_lock is + * to guarantee that the console state is valid (CON_SUSPENDED/CON_ENABLED) + * and that no exit/cleanup routines will run if the console is currently + * undergoing unregistration. * - * Only use this function to read console flags when locklessly - * iterating the console list via srcu. + * If the caller is holding the console_list_lock or it is _certain_ that + * @con is not and will not become registered, the caller may read + * @con->flags directly instead. * * Context: Any context. + * Return: The current value of the @con->flags field. */ static inline short console_srcu_read_flags(const struct console *con) { WARN_ON_ONCE(!console_srcu_read_lock_is_held()); /* - * Locklessly reading console->flags provides a consistent - * read value because there is at most one CPU modifying - * console->flags and that CPU is using only read-modify-write - * operations to do so. + * The READ_ONCE() matches the WRITE_ONCE() when @flags are modified + * for registered consoles with console_srcu_write_flags(). */ return data_race(READ_ONCE(con->flags)); } @@ -477,13 +599,19 @@ static inline bool console_is_registered(const struct console *con) hlist_for_each_entry(con, &console_list, node) #ifdef CONFIG_PRINTK +extern void nbcon_cpu_emergency_enter(void); +extern void nbcon_cpu_emergency_exit(void); extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); +extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt); #else +static inline void nbcon_cpu_emergency_enter(void) { } +static inline void nbcon_cpu_emergency_exit(void) { } static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; } +static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { } #endif extern int console_set_on_cmdline; diff --git a/include/linux/printk.h b/include/linux/printk.h index b937cefcb31c..eca9bb2ee637 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -9,6 +9,8 @@ #include <linux/ratelimit_types.h> #include <linux/once_lite.h> +struct console; + extern const char linux_banner[]; extern const char linux_proc_banner[]; @@ -161,15 +163,16 @@ int _printk(const char *fmt, ...); */ __printf(1, 2) __cold int _printk_deferred(const char *fmt, ...); -extern void __printk_safe_enter(void); -extern void __printk_safe_exit(void); +extern void __printk_deferred_enter(void); +extern void __printk_deferred_exit(void); + /* * The printk_deferred_enter/exit macros are available only as a hack for * some code paths that need to defer all printk console printing. Interrupts * must be disabled for the deferred duration. */ -#define printk_deferred_enter __printk_safe_enter -#define printk_deferred_exit __printk_safe_exit +#define printk_deferred_enter() __printk_deferred_enter() +#define printk_deferred_exit() __printk_deferred_exit() /* * Please don't use printk_ratelimit(), because it shares ratelimiting state @@ -197,6 +200,10 @@ extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold; extern asmlinkage void dump_stack(void) __cold; void printk_trigger_flush(void); void console_try_replay_all(void); +void printk_legacy_allow_panic_sync(void); +extern bool nbcon_device_try_acquire(struct console *con); +extern void nbcon_device_release(struct console *con); +void nbcon_atomic_flush_unsafe(void); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -279,6 +286,24 @@ static inline void printk_trigger_flush(void) static inline void console_try_replay_all(void) { } + +static inline void printk_legacy_allow_panic_sync(void) +{ +} + +static inline bool nbcon_device_try_acquire(struct console *con) +{ + return false; +} + +static inline void nbcon_device_release(struct console *con) +{ +} + +static inline void nbcon_atomic_flush_unsafe(void) +{ +} + #endif bool this_cpu_in_panic(void); diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index aea25eef9a1a..4ab65874a850 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -11,6 +11,8 @@ #include <linux/compiler.h> #include <linux/console.h> #include <linux/interrupt.h> +#include <linux/lockdep.h> +#include <linux/printk.h> #include <linux/spinlock.h> #include <linux/sched.h> #include <linux/tty.h> @@ -590,6 +592,95 @@ struct uart_port { void *private_data; /* generic platform data pointer */ }; +/* + * Only for console->device_lock()/_unlock() callbacks and internal + * port lock wrapper synchronization. + */ +static inline void __uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags) +{ + spin_lock_irqsave(&up->lock, *flags); +} + +/* + * Only for console->device_lock()/_unlock() callbacks and internal + * port lock wrapper synchronization. + */ +static inline void __uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags) +{ + spin_unlock_irqrestore(&up->lock, flags); +} + +/** + * uart_port_set_cons - Safely set the @cons field for a uart + * @up: The uart port to set + * @con: The new console to set to + * + * This function must be used to set @up->cons. It uses the port lock to + * synchronize with the port lock wrappers in order to ensure that the console + * cannot change or disappear while another context is holding the port lock. + */ +static inline void uart_port_set_cons(struct uart_port *up, struct console *con) +{ + unsigned long flags; + + __uart_port_lock_irqsave(up, &flags); + up->cons = con; + __uart_port_unlock_irqrestore(up, flags); +} + +/* Only for internal port lock wrapper usage. */ +static inline bool __uart_port_using_nbcon(struct uart_port *up) +{ + lockdep_assert_held_once(&up->lock); + + if (likely(!uart_console(up))) + return false; + + /* + * @up->cons is only modified under the port lock. Therefore it is + * certain that it cannot disappear here. + * + * @up->cons->node is added/removed from the console list under the + * port lock. Therefore it is certain that the registration status + * cannot change here, thus @up->cons->flags can be read directly. + */ + if (hlist_unhashed_lockless(&up->cons->node) || + !(up->cons->flags & CON_NBCON) || + !up->cons->write_atomic) { + return false; + } + + return true; +} + +/* Only for internal port lock wrapper usage. */ +static inline bool __uart_port_nbcon_try_acquire(struct uart_port *up) +{ + if (!__uart_port_using_nbcon(up)) + return true; + + return nbcon_device_try_acquire(up->cons); +} + +/* Only for internal port lock wrapper usage. */ +static inline void __uart_port_nbcon_acquire(struct uart_port *up) +{ + if (!__uart_port_using_nbcon(up)) + return; + + while (!nbcon_device_try_acquire(up->cons)) + cpu_relax(); +} + +/* Only for internal port lock wrapper usage. */ +static inline void __uart_port_nbcon_release(struct uart_port *up) +{ + if (!__uart_port_using_nbcon(up)) + return; + + nbcon_device_release(up->cons); +} + /** * uart_port_lock - Lock the UART port * @up: Pointer to UART port structure @@ -597,6 +688,7 @@ struct uart_port { static inline void uart_port_lock(struct uart_port *up) { spin_lock(&up->lock); + __uart_port_nbcon_acquire(up); } /** @@ -606,6 +698,7 @@ static inline void uart_port_lock(struct uart_port *up) static inline void uart_port_lock_irq(struct uart_port *up) { spin_lock_irq(&up->lock); + __uart_port_nbcon_acquire(up); } /** @@ -616,6 +709,7 @@ static inline void uart_port_lock_irq(struct uart_port *up) static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags) { spin_lock_irqsave(&up->lock, *flags); + __uart_port_nbcon_acquire(up); } /** @@ -626,7 +720,15 @@ static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *f */ static inline bool uart_port_trylock(struct uart_port *up) { - return spin_trylock(&up->lock); + if (!spin_trylock(&up->lock)) + return false; + + if (!__uart_port_nbcon_try_acquire(up)) { + spin_unlock(&up->lock); + return false; + } + + return true; } /** @@ -638,7 +740,15 @@ static inline bool uart_port_trylock(struct uart_port *up) */ static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long *flags) { - return spin_trylock_irqsave(&up->lock, *flags); + if (!spin_trylock_irqsave(&up->lock, *flags)) + return false; + + if (!__uart_port_nbcon_try_acquire(up)) { + spin_unlock_irqrestore(&up->lock, *flags); + return false; + } + + return true; } /** @@ -647,6 +757,7 @@ static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long */ static inline void uart_port_unlock(struct uart_port *up) { + __uart_port_nbcon_release(up); spin_unlock(&up->lock); } @@ -656,6 +767,7 @@ static inline void uart_port_unlock(struct uart_port *up) */ static inline void uart_port_unlock_irq(struct uart_port *up) { + __uart_port_nbcon_release(up); spin_unlock_irq(&up->lock); } @@ -666,6 +778,7 @@ static inline void uart_port_unlock_irq(struct uart_port *up) */ static inline void uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags) { + __uart_port_nbcon_release(up); spin_unlock_irqrestore(&up->lock, flags); } diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 0349f957e672..7963deac33c3 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -56,6 +56,7 @@ #include <linux/kprobes.h> #include <linux/lockdep.h> #include <linux/context_tracking.h> +#include <linux/console.h> #include <asm/sections.h> @@ -573,8 +574,10 @@ static struct lock_trace *save_trace(void) if (!debug_locks_off_graph_unlock()) return NULL; + nbcon_cpu_emergency_enter(); print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!"); dump_stack(); + nbcon_cpu_emergency_exit(); return NULL; } @@ -887,11 +890,13 @@ look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass) if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) { instrumentation_begin(); debug_locks_off(); + nbcon_cpu_emergency_enter(); printk(KERN_ERR "BUG: looking up invalid subclass: %u\n", subclass); printk(KERN_ERR "turning off the locking correctness validator.\n"); dump_stack(); + nbcon_cpu_emergency_exit(); instrumentation_end(); return NULL; } @@ -968,11 +973,13 @@ static bool assign_lock_key(struct lockdep_map *lock) else { /* Debug-check: all keys must be persistent! */ debug_locks_off(); + nbcon_cpu_emergency_enter(); pr_err("INFO: trying to register non-static key.\n"); pr_err("The code is fine but needs lockdep annotation, or maybe\n"); pr_err("you didn't initialize this object before use?\n"); pr_err("turning off the locking correctness validator.\n"); dump_stack(); + nbcon_cpu_emergency_exit(); return false; } @@ -1316,8 +1323,10 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) return NULL; } + nbcon_cpu_emergency_enter(); print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!"); dump_stack(); + nbcon_cpu_emergency_exit(); return NULL; } nr_lock_classes++; @@ -1349,11 +1358,13 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) if (verbose(class)) { graph_unlock(); + nbcon_cpu_emergency_enter(); printk("\nnew class %px: %s", class->key, class->name); if (class->name_version > 1) printk(KERN_CONT "#%d", class->name_version); printk(KERN_CONT "\n"); dump_stack(); + nbcon_cpu_emergency_exit(); if (!graph_lock()) { return NULL; @@ -1392,8 +1403,10 @@ static struct lock_list *alloc_list_entry(void) if (!debug_locks_off_graph_unlock()) return NULL; + nbcon_cpu_emergency_enter(); print_lockdep_off("BUG: MAX_LOCKDEP_ENTRIES too low!"); dump_stack(); + nbcon_cpu_emergency_exit(); return NULL; } nr_list_entries++; @@ -2039,6 +2052,8 @@ static noinline void print_circular_bug(struct lock_list *this, depth = get_lock_depth(target); + nbcon_cpu_emergency_enter(); + print_circular_bug_header(target, depth, check_src, check_tgt); parent = get_lock_parent(target); @@ -2057,6 +2072,8 @@ static noinline void print_circular_bug(struct lock_list *this, printk("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } static noinline void print_bfs_bug(int ret) @@ -2569,6 +2586,8 @@ print_bad_irq_dependency(struct task_struct *curr, if (!debug_locks_off_graph_unlock() || debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("=====================================================\n"); pr_warn("WARNING: %s-safe -> %s-unsafe lock order detected\n", @@ -2618,11 +2637,13 @@ print_bad_irq_dependency(struct task_struct *curr, pr_warn(" and %s-irq-unsafe lock:\n", irqclass); next_root->trace = save_trace(); if (!next_root->trace) - return; + goto out; print_shortest_lock_dependencies(forwards_entry, next_root); pr_warn("\nstack backtrace:\n"); dump_stack(); +out: + nbcon_cpu_emergency_exit(); } static const char *state_names[] = { @@ -2987,6 +3008,8 @@ print_deadlock_bug(struct task_struct *curr, struct held_lock *prev, if (!debug_locks_off_graph_unlock() || debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("============================================\n"); pr_warn("WARNING: possible recursive locking detected\n"); @@ -3009,6 +3032,8 @@ print_deadlock_bug(struct task_struct *curr, struct held_lock *prev, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } /* @@ -3606,6 +3631,8 @@ static void print_collision(struct task_struct *curr, struct held_lock *hlock_next, struct lock_chain *chain) { + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("============================\n"); pr_warn("WARNING: chain_key collision\n"); @@ -3622,6 +3649,8 @@ static void print_collision(struct task_struct *curr, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } #endif @@ -3712,8 +3741,10 @@ static inline int add_chain_cache(struct task_struct *curr, if (!debug_locks_off_graph_unlock()) return 0; + nbcon_cpu_emergency_enter(); print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!"); dump_stack(); + nbcon_cpu_emergency_exit(); return 0; } chain->chain_key = chain_key; @@ -3730,8 +3761,10 @@ static inline int add_chain_cache(struct task_struct *curr, if (!debug_locks_off_graph_unlock()) return 0; + nbcon_cpu_emergency_enter(); print_lockdep_off("BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!"); dump_stack(); + nbcon_cpu_emergency_exit(); return 0; } @@ -3970,6 +4003,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this, if (!debug_locks_off() || debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("================================\n"); pr_warn("WARNING: inconsistent lock state\n"); @@ -3998,6 +4033,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } /* @@ -4032,6 +4069,8 @@ print_irq_inversion_bug(struct task_struct *curr, if (!debug_locks_off_graph_unlock() || debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("========================================================\n"); pr_warn("WARNING: possible irq lock inversion dependency detected\n"); @@ -4072,11 +4111,13 @@ print_irq_inversion_bug(struct task_struct *curr, pr_warn("\nthe shortest dependencies between 2nd lock and 1st lock:\n"); root->trace = save_trace(); if (!root->trace) - return; + goto out; print_shortest_lock_dependencies(other, root); pr_warn("\nstack backtrace:\n"); dump_stack(); +out: + nbcon_cpu_emergency_exit(); } /* @@ -4153,6 +4194,8 @@ void print_irqtrace_events(struct task_struct *curr) { const struct irqtrace_events *trace = &curr->irqtrace; + nbcon_cpu_emergency_enter(); + printk("irq event stamp: %u\n", trace->irq_events); printk("hardirqs last enabled at (%u): [<%px>] %pS\n", trace->hardirq_enable_event, (void *)trace->hardirq_enable_ip, @@ -4166,6 +4209,8 @@ void print_irqtrace_events(struct task_struct *curr) printk("softirqs last disabled at (%u): [<%px>] %pS\n", trace->softirq_disable_event, (void *)trace->softirq_disable_ip, (void *)trace->softirq_disable_ip); + + nbcon_cpu_emergency_exit(); } static int HARDIRQ_verbose(struct lock_class *class) @@ -4686,10 +4731,12 @@ unlock: * We must printk outside of the graph_lock: */ if (ret == 2) { + nbcon_cpu_emergency_enter(); printk("\nmarked lock as {%s}:\n", usage_str[new_bit]); print_lock(this); print_irqtrace_events(curr); dump_stack(); + nbcon_cpu_emergency_exit(); } return ret; @@ -4730,6 +4777,8 @@ print_lock_invalid_wait_context(struct task_struct *curr, if (debug_locks_silent) return 0; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("=============================\n"); pr_warn("[ BUG: Invalid wait context ]\n"); @@ -4749,6 +4798,8 @@ print_lock_invalid_wait_context(struct task_struct *curr, pr_warn("stack backtrace:\n"); dump_stack(); + nbcon_cpu_emergency_exit(); + return 0; } @@ -4956,6 +5007,8 @@ print_lock_nested_lock_not_held(struct task_struct *curr, if (debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("==================================\n"); pr_warn("WARNING: Nested lock was not taken\n"); @@ -4976,6 +5029,8 @@ print_lock_nested_lock_not_held(struct task_struct *curr, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } static int __lock_is_held(const struct lockdep_map *lock, int read); @@ -5024,11 +5079,13 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, debug_class_ops_inc(class); if (very_verbose(class)) { + nbcon_cpu_emergency_enter(); printk("\nacquire class [%px] %s", class->key, class->name); if (class->name_version > 1) printk(KERN_CONT "#%d", class->name_version); printk(KERN_CONT "\n"); dump_stack(); + nbcon_cpu_emergency_exit(); } /* @@ -5155,6 +5212,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, #endif if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) { debug_locks_off(); + nbcon_cpu_emergency_enter(); print_lockdep_off("BUG: MAX_LOCK_DEPTH too low!"); printk(KERN_DEBUG "depth: %i max: %lu!\n", curr->lockdep_depth, MAX_LOCK_DEPTH); @@ -5162,6 +5220,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, lockdep_print_held_locks(current); debug_show_all_locks(); dump_stack(); + nbcon_cpu_emergency_exit(); return 0; } @@ -5181,6 +5240,8 @@ static void print_unlock_imbalance_bug(struct task_struct *curr, if (debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("=====================================\n"); pr_warn("WARNING: bad unlock balance detected!\n"); @@ -5197,6 +5258,8 @@ static void print_unlock_imbalance_bug(struct task_struct *curr, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } static noinstr int match_held_lock(const struct held_lock *hlock, @@ -5901,6 +5964,8 @@ static void print_lock_contention_bug(struct task_struct *curr, if (debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("=================================\n"); pr_warn("WARNING: bad contention detected!\n"); @@ -5917,6 +5982,8 @@ static void print_lock_contention_bug(struct task_struct *curr, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } static void @@ -6536,6 +6603,8 @@ print_freed_lock_bug(struct task_struct *curr, const void *mem_from, if (debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("=========================\n"); pr_warn("WARNING: held lock freed!\n"); @@ -6548,6 +6617,8 @@ print_freed_lock_bug(struct task_struct *curr, const void *mem_from, pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } static inline int not_in_range(const void* mem_from, unsigned long mem_len, @@ -6594,6 +6665,8 @@ static void print_held_locks_bug(void) if (debug_locks_silent) return; + nbcon_cpu_emergency_enter(); + pr_warn("\n"); pr_warn("====================================\n"); pr_warn("WARNING: %s/%d still has locks held!\n", @@ -6603,6 +6676,8 @@ static void print_held_locks_bug(void) lockdep_print_held_locks(current); pr_warn("\nstack backtrace:\n"); dump_stack(); + + nbcon_cpu_emergency_exit(); } void debug_check_no_locks_held(void) @@ -6660,6 +6735,7 @@ asmlinkage __visible void lockdep_sys_exit(void) if (unlikely(curr->lockdep_depth)) { if (!debug_locks_off()) return; + nbcon_cpu_emergency_enter(); pr_warn("\n"); pr_warn("================================================\n"); pr_warn("WARNING: lock held when returning to user space!\n"); @@ -6668,6 +6744,7 @@ asmlinkage __visible void lockdep_sys_exit(void) pr_warn("%s/%d is leaving the kernel with locks still held!\n", curr->comm, curr->pid); lockdep_print_held_locks(curr); + nbcon_cpu_emergency_exit(); } /* @@ -6684,6 +6761,7 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s) bool rcu = warn_rcu_enter(); /* Note: the following can be executed concurrently, so be careful. */ + nbcon_cpu_emergency_enter(); pr_warn("\n"); pr_warn("=============================\n"); pr_warn("WARNING: suspicious RCU usage\n"); @@ -6722,6 +6800,7 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s) lockdep_print_held_locks(curr); pr_warn("\nstack backtrace:\n"); dump_stack(); + nbcon_cpu_emergency_exit(); warn_rcu_exit(rcu); } EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious); diff --git a/kernel/panic.c b/kernel/panic.c index 2a0449144f82..753d12f4dc8f 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -374,6 +374,8 @@ void panic(const char *fmt, ...) panic_other_cpus_shutdown(_crash_kexec_post_notifiers); + printk_legacy_allow_panic_sync(); + /* * Run any panic handlers, including those that might need to * add information to the kmsg dump output. @@ -463,6 +465,7 @@ void panic(const char *fmt, ...) * Explicitly flush the kernel log buffer one last time. */ console_flush_on_panic(CONSOLE_FLUSH_PENDING); + nbcon_atomic_flush_unsafe(); local_irq_enable(); for (i = 0; ; i += PANIC_TIMER_STEP) { @@ -682,6 +685,7 @@ bool oops_may_print(void) */ void oops_enter(void) { + nbcon_cpu_emergency_enter(); tracing_off(); /* can't trust the integrity of the kernel anymore: */ debug_locks_off(); @@ -704,6 +708,7 @@ void oops_exit(void) { do_oops_enter_exit(); print_oops_end_marker(); + nbcon_cpu_emergency_exit(); kmsg_dump(KMSG_DUMP_OOPS); } @@ -715,6 +720,8 @@ struct warn_args { void __warn(const char *file, int line, void *caller, unsigned taint, struct pt_regs *regs, struct warn_args *args) { + nbcon_cpu_emergency_enter(); + disable_trace_on_warning(); if (file) @@ -750,6 +757,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint, /* Just a warning, don't kill lockdep. */ add_taint(taint, LOCKDEP_STILL_OK); + + nbcon_cpu_emergency_exit(); } #ifdef CONFIG_BUG diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 19dcc5832651..3fcb48502adb 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -2,11 +2,12 @@ /* * internal.h - printk internal definitions */ -#include <linux/percpu.h> #include <linux/console.h> -#include "printk_ringbuffer.h" +#include <linux/percpu.h> +#include <linux/types.h> #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL) +struct ctl_table; void __init printk_sysctl_init(void); int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos); @@ -20,6 +21,19 @@ int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write, (con->flags & CON_BOOT) ? "boot" : "", \ con->name, con->index, ##__VA_ARGS__) +/* + * Identify if legacy printing is forced in a dedicated kthread. If + * true, all printing via console lock occurs within a dedicated + * legacy printer thread. The only exception is on panic, after the + * nbcon consoles have had their chance to print the panic messages + * first. + */ +#ifdef CONFIG_PREEMPT_RT +# define force_legacy_kthread() (true) +#else +# define force_legacy_kthread() (false) +#endif + #ifdef CONFIG_PRINTK #ifdef CONFIG_PRINTK_CALLER @@ -43,7 +57,11 @@ enum printk_info_flags { LOG_CONT = 8, /* text is a fragment of a continuation line */ }; +struct printk_ringbuffer; +struct dev_printk_info; + extern struct printk_ringbuffer *prb; +extern bool printk_kthreads_running; __printf(4, 0) int vprintk_store(int facility, int level, @@ -53,6 +71,9 @@ int vprintk_store(int facility, int level, __printf(1, 0) int vprintk_default(const char *fmt, va_list args); __printf(1, 0) int vprintk_deferred(const char *fmt, va_list args); +void __printk_safe_enter(void); +void __printk_safe_exit(void); + bool printk_percpu_data_ready(void); #define printk_safe_enter_irqsave(flags) \ @@ -68,15 +89,85 @@ bool printk_percpu_data_ready(void); } while (0) void defer_console_output(void); +bool is_printk_legacy_deferred(void); u16 printk_parse_prefix(const char *text, int *level, enum printk_info_flags *flags); +void console_lock_spinning_enable(void); +int console_lock_spinning_disable_and_check(int cookie); u64 nbcon_seq_read(struct console *con); void nbcon_seq_force(struct console *con, u64 seq); bool nbcon_alloc(struct console *con); -void nbcon_init(struct console *con); void nbcon_free(struct console *con); +enum nbcon_prio nbcon_get_default_prio(void); +void nbcon_atomic_flush_pending(void); +bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, + int cookie, bool use_atomic); +bool nbcon_kthread_create(struct console *con); +void nbcon_kthread_stop(struct console *con); +void nbcon_kthreads_wake(void); + +/* + * Check if the given console is currently capable and allowed to print + * records. Note that this function does not consider the current context, + * which can also play a role in deciding if @con can be used to print + * records. + */ +static inline bool console_is_usable(struct console *con, short flags, bool use_atomic) +{ + if (!(flags & CON_ENABLED)) + return false; + + if ((flags & CON_SUSPENDED)) + return false; + + if (flags & CON_NBCON) { + /* The write_atomic() callback is optional. */ + if (use_atomic && !con->write_atomic) + return false; + + /* + * For the !use_atomic case, @printk_kthreads_running is not + * checked because the write_thread() callback is also used + * via the legacy loop when the printer threads are not + * available. + */ + } else { + if (!con->write) + return false; + } + + /* + * Console drivers may assume that per-cpu resources have been + * allocated. So unless they're explicitly marked as being able to + * cope (CON_ANYTIME) don't call them until this CPU is officially up. + */ + if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME)) + return false; + + return true; +} + +/** + * nbcon_kthread_wake - Wake up a console printing thread + * @con: Console to operate on + */ +static inline void nbcon_kthread_wake(struct console *con) +{ + /* + * Guarantee any new records can be seen by tasks preparing to wait + * before this context checks if the rcuwait is empty. + * + * The full memory barrier in rcuwait_wake_up() pairs with the full + * memory barrier within set_current_state() of + * ___rcuwait_wait_event(), which is called after prepare_to_rcuwait() + * adds the waiter but before it has checked the wait condition. + * + * This pairs with nbcon_kthread_func:A. + */ + rcuwait_wake_up(&con->rcuwait); /* LMM(nbcon_kthread_wake:A) */ +} #else @@ -84,6 +175,8 @@ void nbcon_free(struct console *con); #define PRINTK_MESSAGE_MAX 0 #define PRINTKRB_RECORD_MAX 0 +#define printk_kthreads_running (false) + /* * In !PRINTK builds we still export console_sem * semaphore and some of console functions (console_unlock()/etc.), so @@ -93,14 +186,119 @@ void nbcon_free(struct console *con); #define printk_safe_exit_irqrestore(flags) local_irq_restore(flags) static inline bool printk_percpu_data_ready(void) { return false; } +static inline void defer_console_output(void) { } +static inline bool is_printk_legacy_deferred(void) { return false; } static inline u64 nbcon_seq_read(struct console *con) { return 0; } static inline void nbcon_seq_force(struct console *con, u64 seq) { } static inline bool nbcon_alloc(struct console *con) { return false; } -static inline void nbcon_init(struct console *con) { } static inline void nbcon_free(struct console *con) { } +static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; } +static inline void nbcon_atomic_flush_pending(void) { } +static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, + int cookie, bool use_atomic) { return false; } +static inline void nbcon_kthread_wake(struct console *con) { } +static inline void nbcon_kthreads_wake(void) { } + +static inline bool console_is_usable(struct console *con, short flags, + bool use_atomic) { return false; } #endif /* CONFIG_PRINTK */ +extern bool have_boot_console; +extern bool have_nbcon_console; +extern bool have_legacy_console; +extern bool legacy_allow_panic_sync; + +/** + * struct console_flush_type - Define available console flush methods + * @nbcon_atomic: Flush directly using nbcon_atomic() callback + * @nbcon_offload: Offload flush to printer thread + * @legacy_direct: Call the legacy loop in this context + * @legacy_offload: Offload the legacy loop into IRQ or legacy thread + * + * Note that the legacy loop also flushes the nbcon consoles. + */ +struct console_flush_type { + bool nbcon_atomic; + bool nbcon_offload; + bool legacy_direct; + bool legacy_offload; +}; + +/* + * Identify which console flushing methods should be used in the context of + * the caller. + */ +static inline void printk_get_console_flush_type(struct console_flush_type *ft) +{ + memset(ft, 0, sizeof(*ft)); + + switch (nbcon_get_default_prio()) { + case NBCON_PRIO_NORMAL: + if (have_nbcon_console && !have_boot_console) { + if (printk_kthreads_running) + ft->nbcon_offload = true; + else + ft->nbcon_atomic = true; + } + + /* Legacy consoles are flushed directly when possible. */ + if (have_legacy_console || have_boot_console) { + if (!is_printk_legacy_deferred()) + ft->legacy_direct = true; + else + ft->legacy_offload = true; + } + break; + + case NBCON_PRIO_EMERGENCY: + if (have_nbcon_console && !have_boot_console) + ft->nbcon_atomic = true; + + /* Legacy consoles are flushed directly when possible. */ + if (have_legacy_console || have_boot_console) { + if (!is_printk_legacy_deferred()) + ft->legacy_direct = true; + else + ft->legacy_offload = true; + } + break; + + case NBCON_PRIO_PANIC: + /* + * In panic, the nbcon consoles will directly print. But + * only allowed if there are no boot consoles. + */ + if (have_nbcon_console && !have_boot_console) + ft->nbcon_atomic = true; + + if (have_legacy_console || have_boot_console) { + /* + * This is the same decision as NBCON_PRIO_NORMAL + * except that offloading never occurs in panic. + * + * Note that console_flush_on_panic() will flush + * legacy consoles anyway, even if unsafe. + */ + if (!is_printk_legacy_deferred()) + ft->legacy_direct = true; + + /* + * In panic, if nbcon atomic printing occurs, + * the legacy consoles must remain silent until + * explicitly allowed. + */ + if (ft->nbcon_atomic && !legacy_allow_panic_sync) + ft->legacy_direct = false; + } + break; + + default: + WARN_ON_ONCE(1); + break; + } +} + extern struct printk_buffers printk_shared_pbufs; /** @@ -135,4 +333,5 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq, #ifdef CONFIG_PRINTK void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped); +void console_prepend_replay(struct printk_message *pmsg); #endif diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index c8093bcc01fe..fd12efcc4aed 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -2,11 +2,25 @@ // Copyright (C) 2022 Linutronix GmbH, John Ogness // Copyright (C) 2022 Intel, Thomas Gleixner -#include <linux/kernel.h> +#include <linux/atomic.h> +#include <linux/bug.h> #include <linux/console.h> #include <linux/delay.h> +#include <linux/errno.h> +#include <linux/export.h> +#include <linux/init.h> +#include <linux/irqflags.h> +#include <linux/kthread.h> +#include <linux/minmax.h> +#include <linux/percpu.h> +#include <linux/preempt.h> #include <linux/slab.h> +#include <linux/smp.h> +#include <linux/stddef.h> +#include <linux/string.h> +#include <linux/types.h> #include "internal.h" +#include "printk_ringbuffer.h" /* * Printk console printing implementation for consoles which does not depend * on the legacy style console_lock mechanism. @@ -172,9 +186,6 @@ void nbcon_seq_force(struct console *con, u64 seq) u64 valid_seq = max_t(u64, seq, prb_first_valid_seq(prb)); atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), __u64seq_to_ulseq(valid_seq)); - - /* Clear con->seq since nbcon consoles use con->nbcon_seq instead. */ - con->seq = 0; } /** @@ -231,6 +242,13 @@ static int nbcon_context_try_acquire_direct(struct nbcon_context *ctxt, struct nbcon_state new; do { + /* + * Panic does not imply that the console is owned. However, it + * is critical that non-panic CPUs during panic are unable to + * acquire ownership in order to satisfy the assumptions of + * nbcon_waiter_matches(). In particular, the assumption that + * lower priorities are ignored during panic. + */ if (other_cpu_in_panic()) return -EPERM; @@ -262,18 +280,29 @@ static bool nbcon_waiter_matches(struct nbcon_state *cur, int expected_prio) /* * The request context is well defined by the @req_prio because: * - * - Only a context with a higher priority can take over the request. + * - Only a context with a priority higher than the owner can become + * a waiter. + * - Only a context with a priority higher than the waiter can + * directly take over the request. * - There are only three priorities. * - Only one CPU is allowed to request PANIC priority. * - Lower priorities are ignored during panic() until reboot. * * As a result, the following scenario is *not* possible: * - * 1. Another context with a higher priority directly takes ownership. - * 2. The higher priority context releases the ownership. - * 3. A lower priority context takes the ownership. - * 4. Another context with the same priority as this context + * 1. This context is currently a waiter. + * 2. Another context with a higher priority than this context + * directly takes ownership. + * 3. The higher priority context releases the ownership. + * 4. Another lower priority context takes the ownership. + * 5. Another context with the same priority as this context * creates a request and starts waiting. + * + * Event #1 implies this context is EMERGENCY. + * Event #2 implies the new context is PANIC. + * Event #3 occurs when panic() has flushed the console. + * Events #4 and #5 are not possible due to the other_cpu_in_panic() + * check in nbcon_context_try_acquire_direct(). */ return (cur->req_prio == expected_prio); @@ -531,6 +560,7 @@ static struct printk_buffers panic_nbcon_pbufs; * nbcon_context_try_acquire - Try to acquire nbcon console * @ctxt: The context of the caller * + * Context: Under @ctxt->con->device_lock() or local_irq_save(). * Return: True if the console was acquired. False otherwise. * * If the caller allowed an unsafe hostile takeover, on success the @@ -538,7 +568,6 @@ static struct printk_buffers panic_nbcon_pbufs; * in an unsafe state. Otherwise, on success the caller may assume * the console is not in an unsafe state. */ -__maybe_unused static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) { unsigned int cpu = smp_processor_id(); @@ -581,11 +610,29 @@ static bool nbcon_owner_matches(struct nbcon_state *cur, int expected_cpu, int expected_prio) { /* - * Since consoles can only be acquired by higher priorities, - * owning contexts are uniquely identified by @prio. However, - * since contexts can unexpectedly lose ownership, it is - * possible that later another owner appears with the same - * priority. For this reason @cpu is also needed. + * A similar function, nbcon_waiter_matches(), only deals with + * EMERGENCY and PANIC priorities. However, this function must also + * deal with the NORMAL priority, which requires additional checks + * and constraints. + * + * For the case where preemption and interrupts are disabled, it is + * enough to also verify that the owning CPU has not changed. + * + * For the case where preemption or interrupts are enabled, an + * external synchronization method *must* be used. In particular, + * the driver-specific locking mechanism used in device_lock() + * (including disabling migration) should be used. It prevents + * scenarios such as: + * + * 1. [Task A] owns a context with NBCON_PRIO_NORMAL on [CPU X] and + * is scheduled out. + * 2. Another context takes over the lock with NBCON_PRIO_EMERGENCY + * and releases it. + * 3. [Task B] acquires a context with NBCON_PRIO_NORMAL on [CPU X] + * and is scheduled out. + * 4. [Task A] gets running on [CPU X] and sees that the console is + * still owned by a task on [CPU X] with NBON_PRIO_NORMAL. Thus + * [Task A] thinks it is the owner when it is not. */ if (cur->prio != expected_prio) @@ -784,6 +831,19 @@ out: return nbcon_context_can_proceed(ctxt, &cur); } +static void nbcon_write_context_set_buf(struct nbcon_write_context *wctxt, + char *buf, unsigned int len) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con = ctxt->console; + struct nbcon_state cur; + + wctxt->outbuf = buf; + wctxt->len = len; + nbcon_state_read(con, &cur); + wctxt->unsafe_takeover = cur.unsafe_takeover; +} + /** * nbcon_enter_unsafe - Enter an unsafe region in the driver * @wctxt: The write context that was handed to the write function @@ -799,8 +859,12 @@ out: bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + bool is_owner; - return nbcon_context_enter_unsafe(ctxt); + is_owner = nbcon_context_enter_unsafe(ctxt); + if (!is_owner) + nbcon_write_context_set_buf(wctxt, NULL, 0); + return is_owner; } EXPORT_SYMBOL_GPL(nbcon_enter_unsafe); @@ -819,14 +883,47 @@ EXPORT_SYMBOL_GPL(nbcon_enter_unsafe); bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + bool ret; - return nbcon_context_exit_unsafe(ctxt); + ret = nbcon_context_exit_unsafe(ctxt); + if (!ret) + nbcon_write_context_set_buf(wctxt, NULL, 0); + return ret; } EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); /** + * nbcon_reacquire_nobuf - Reacquire a console after losing ownership + * while printing + * @wctxt: The write context that was handed to the write callback + * + * Since ownership can be lost at any time due to handover or takeover, a + * printing context _must_ be prepared to back out immediately and + * carefully. However, there are scenarios where the printing context must + * reacquire ownership in order to finalize or revert hardware changes. + * + * This function allows a printing context to reacquire ownership using the + * same priority as its previous ownership. + * + * Note that after a successful reacquire the printing context will have no + * output buffer because that has been lost. This function cannot be used to + * resume printing. + */ +void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + + while (!nbcon_context_try_acquire(ctxt)) + cpu_relax(); + + nbcon_write_context_set_buf(wctxt, NULL, 0); +} +EXPORT_SYMBOL_GPL(nbcon_reacquire_nobuf); + +/** * nbcon_emit_next_record - Emit a record in the acquired context * @wctxt: The write context that will be handed to the write function + * @use_atomic: True if the write_atomic() callback is to be used * * Return: True if this context still owns the console. False if * ownership was handed over or taken. @@ -840,8 +937,7 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); * When true is returned, @wctxt->ctxt.backlog indicates whether there are * still records pending in the ringbuffer, */ -__maybe_unused -static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) +static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_atomic) { struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); struct console *con = ctxt->console; @@ -852,7 +948,22 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) unsigned long con_dropped; struct nbcon_state cur; unsigned long dropped; - bool done; + unsigned long ulseq; + + /* + * This function should never be called for consoles that have not + * implemented the necessary callback for writing: i.e. legacy + * consoles and, when atomic, nbcon consoles with no write_atomic(). + * Handle it as if ownership was lost and try to continue. + * + * Note that for nbcon consoles the write_thread() callback is + * mandatory and was already checked in nbcon_alloc(). + */ + if (WARN_ON_ONCE((use_atomic && !con->write_atomic) || + !(console_srcu_read_flags(con) & CON_NBCON))) { + nbcon_context_release(ctxt); + return false; + } /* * The printk buffers are filled within an unsafe section. This @@ -878,6 +989,29 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) if (dropped && !is_extended) console_prepend_dropped(&pmsg, dropped); + /* + * If the previous owner was assigned the same record, this context + * has taken over ownership and is replaying the record. Prepend a + * message to let the user know the record is replayed. + */ + ulseq = atomic_long_read(&ACCESS_PRIVATE(con, nbcon_prev_seq)); + if (__ulseq_to_u64seq(prb, ulseq) == pmsg.seq) { + console_prepend_replay(&pmsg); + } else { + /* + * Ensure this context is still the owner before trying to + * update @nbcon_prev_seq. Otherwise the value in @ulseq may + * not be from the previous owner and instead be some later + * value from the context that took over ownership. + */ + nbcon_state_read(con, &cur); + if (!nbcon_context_can_proceed(ctxt, &cur)) + return false; + + atomic_long_try_cmpxchg(&ACCESS_PRIVATE(con, nbcon_prev_seq), &ulseq, + __u64seq_to_ulseq(pmsg.seq)); + } + if (!nbcon_context_exit_unsafe(ctxt)) return false; @@ -886,22 +1020,27 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) goto update_con; /* Initialize the write context for driver callbacks. */ - wctxt->outbuf = &pmsg.pbufs->outbuf[0]; - wctxt->len = pmsg.outbuf_len; - nbcon_state_read(con, &cur); - wctxt->unsafe_takeover = cur.unsafe_takeover; + nbcon_write_context_set_buf(wctxt, &pmsg.pbufs->outbuf[0], pmsg.outbuf_len); - if (con->write_atomic) { - done = con->write_atomic(con, wctxt); - } else { + if (use_atomic) + con->write_atomic(con, wctxt); + else + con->write_thread(con, wctxt); + + if (!wctxt->outbuf) { + /* + * Ownership was lost and reacquired by the driver. Handle it + * as if ownership was lost. + */ nbcon_context_release(ctxt); - WARN_ON_ONCE(1); - done = false; + return false; } - /* If not done, the emit was aborted. */ - if (!done) - return false; + /* + * Ownership may have been lost but _not_ reacquired by the driver. + * This case is detected and handled when entering unsafe to update + * dropped/seq values. + */ /* * Since any dropped message was successfully output, reset the @@ -928,54 +1067,650 @@ update_con: return nbcon_context_exit_unsafe(ctxt); } +/* + * nbcon_emit_one - Print one record for an nbcon console using the + * specified callback + * @wctxt: An initialized write context struct to use for this context + * @use_atomic: True if the write_atomic() callback is to be used + * + * Return: True, when a record has been printed and there are still + * pending records. The caller might want to continue flushing. + * + * False, when there is no pending record, or when the console + * context cannot be acquired, or the ownership has been lost. + * The caller should give up. Either the job is done, cannot be + * done, or will be handled by the owning context. + * + * This is an internal helper to handle the locking of the console before + * calling nbcon_emit_next_record(). + */ +static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con = ctxt->console; + unsigned long flags; + bool ret = false; + + if (!use_atomic) { + con->device_lock(con, &flags); + + /* + * Ensure this stays on the CPU to make handover and + * takeover possible. + */ + cant_migrate(); + } + + if (!nbcon_context_try_acquire(ctxt)) + goto out; + + /* + * nbcon_emit_next_record() returns false when the console was + * handed over or taken over. In both cases the context is no + * longer valid. + * + * The higher priority printing context takes over responsibility + * to print the pending records. + */ + if (!nbcon_emit_next_record(wctxt, use_atomic)) + goto out; + + nbcon_context_release(ctxt); + + ret = ctxt->backlog; +out: + if (!use_atomic) + con->device_unlock(con, flags); + return ret; +} + /** - * nbcon_alloc - Allocate buffers needed by the nbcon console - * @con: Console to allocate buffers for + * nbcon_kthread_should_wakeup - Check whether a printer thread should wakeup + * @con: Console to operate on + * @ctxt: The nbcon context from nbcon_context_try_acquire() * - * Return: True on success. False otherwise and the console cannot - * be used. + * Return: True if the thread should shutdown or if the console is + * allowed to print and a record is available. False otherwise. * - * This is not part of nbcon_init() because buffer allocation must - * be performed earlier in the console registration process. + * After the thread wakes up, it must first check if it should shutdown before + * attempting any printing. */ -bool nbcon_alloc(struct console *con) +static bool nbcon_kthread_should_wakeup(struct console *con, struct nbcon_context *ctxt) { - if (con->flags & CON_BOOT) { + bool ret = false; + short flags; + int cookie; + + if (kthread_should_stop()) + return true; + + cookie = console_srcu_read_lock(); + + flags = console_srcu_read_flags(con); + if (console_is_usable(con, flags, false)) { + /* Bring the sequence in @ctxt up to date */ + ctxt->seq = nbcon_seq_read(con); + + ret = prb_read_valid(prb, ctxt->seq, NULL); + } + + console_srcu_read_unlock(cookie); + return ret; +} + +/** + * nbcon_kthread_func - The printer thread function + * @__console: Console to operate on + * + * Return: 0 + */ +static int nbcon_kthread_func(void *__console) +{ + struct console *con = __console; + struct nbcon_write_context wctxt = { + .ctxt.console = con, + .ctxt.prio = NBCON_PRIO_NORMAL, + }; + struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); + short con_flags; + bool backlog; + int cookie; + +wait_for_event: + /* + * Guarantee this task is visible on the rcuwait before + * checking the wake condition. + * + * The full memory barrier within set_current_state() of + * ___rcuwait_wait_event() pairs with the full memory + * barrier within rcuwait_has_sleeper(). + * + * This pairs with rcuwait_has_sleeper:A and nbcon_kthread_wake:A. + */ + rcuwait_wait_event(&con->rcuwait, + nbcon_kthread_should_wakeup(con, ctxt), + TASK_INTERRUPTIBLE); /* LMM(nbcon_kthread_func:A) */ + + do { + if (kthread_should_stop()) + return 0; + + backlog = false; + /* - * Boot console printing is synchronized with legacy console - * printing, so boot consoles can share the same global printk - * buffers. + * Keep the srcu read lock around the entire operation so that + * synchronize_srcu() can guarantee that the kthread stopped + * or suspended printing. */ - con->pbufs = &printk_shared_pbufs; + cookie = console_srcu_read_lock(); + + con_flags = console_srcu_read_flags(con); + + if (console_is_usable(con, con_flags, false)) + backlog = nbcon_emit_one(&wctxt, false); + + console_srcu_read_unlock(cookie); + + cond_resched(); + + } while (backlog); + + goto wait_for_event; +} + +/** + * nbcon_irq_work - irq work to wake console printer thread + * @irq_work: The irq work to operate on + */ +static void nbcon_irq_work(struct irq_work *irq_work) +{ + struct console *con = container_of(irq_work, struct console, irq_work); + + nbcon_kthread_wake(con); +} + +static inline bool rcuwait_has_sleeper(struct rcuwait *w) +{ + /* + * Guarantee any new records can be seen by tasks preparing to wait + * before this context checks if the rcuwait is empty. + * + * This full memory barrier pairs with the full memory barrier within + * set_current_state() of ___rcuwait_wait_event(), which is called + * after prepare_to_rcuwait() adds the waiter but before it has + * checked the wait condition. + * + * This pairs with nbcon_kthread_func:A. + */ + smp_mb(); /* LMM(rcuwait_has_sleeper:A) */ + return rcuwait_active(w); +} + +/** + * nbcon_kthreads_wake - Wake up printing threads using irq_work + */ +void nbcon_kthreads_wake(void) +{ + struct console *con; + int cookie; + + if (!printk_kthreads_running) + return; + + cookie = console_srcu_read_lock(); + for_each_console_srcu(con) { + if (!(console_srcu_read_flags(con) & CON_NBCON)) + continue; + + /* + * Only schedule irq_work if the printing thread is + * actively waiting. If not waiting, the thread will + * notice by itself that it has work to do. + */ + if (rcuwait_has_sleeper(&con->rcuwait)) + irq_work_queue(&con->irq_work); + } + console_srcu_read_unlock(cookie); +} + +/* + * nbcon_kthread_stop - Stop a console printer thread + * @con: Console to operate on + */ +void nbcon_kthread_stop(struct console *con) +{ + lockdep_assert_console_list_lock_held(); + + if (!con->kthread) + return; + + kthread_stop(con->kthread); + con->kthread = NULL; +} + +/** + * nbcon_kthread_create - Create a console printer thread + * @con: Console to operate on + * + * Return: True if the kthread was started or already exists. + * Otherwise false and @con must not be registered. + * + * This function is called when it will be expected that nbcon consoles are + * flushed using the kthread. The messages printed with NBCON_PRIO_NORMAL + * will be no longer flushed by the legacy loop. This is why failure must + * be fatal for console registration. + * + * If @con was already registered and this function fails, @con must be + * unregistered before the global state variable @printk_kthreads_running + * can be set. + */ +bool nbcon_kthread_create(struct console *con) +{ + struct task_struct *kt; + + lockdep_assert_console_list_lock_held(); + + if (con->kthread) + return true; + + kt = kthread_run(nbcon_kthread_func, con, "pr/%s%d", con->name, con->index); + if (WARN_ON(IS_ERR(kt))) { + con_printk(KERN_ERR, con, "failed to start printing thread\n"); + return false; + } + + con->kthread = kt; + + /* + * It is important that console printing threads are scheduled + * shortly after a printk call and with generous runtime budgets. + */ + sched_set_normal(con->kthread, -20); + + return true; +} + +/* Track the nbcon emergency nesting per CPU. */ +static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting); +static unsigned int early_nbcon_pcpu_emergency_nesting __initdata; + +/** + * nbcon_get_cpu_emergency_nesting - Get the per CPU emergency nesting pointer + * + * Context: For reading, any context. For writing, any context which could + * not be migrated to another CPU. + * Return: Either a pointer to the per CPU emergency nesting counter of + * the current CPU or to the init data during early boot. + * + * The function is safe for reading per-CPU variables in any context because + * preemption is disabled if the current CPU is in the emergency state. See + * also nbcon_cpu_emergency_enter(). + */ +static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void) +{ + /* + * The value of __printk_percpu_data_ready gets set in normal + * context and before SMP initialization. As a result it could + * never change while inside an nbcon emergency section. + */ + if (!printk_percpu_data_ready()) + return &early_nbcon_pcpu_emergency_nesting; + + return raw_cpu_ptr(&nbcon_pcpu_emergency_nesting); +} + +/** + * nbcon_get_default_prio - The appropriate nbcon priority to use for nbcon + * printing on the current CPU + * + * Context: Any context. + * Return: The nbcon_prio to use for acquiring an nbcon console in this + * context for printing. + * + * The function is safe for reading per-CPU data in any context because + * preemption is disabled if the current CPU is in the emergency or panic + * state. + */ +enum nbcon_prio nbcon_get_default_prio(void) +{ + unsigned int *cpu_emergency_nesting; + + if (this_cpu_in_panic()) + return NBCON_PRIO_PANIC; + + cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting(); + if (*cpu_emergency_nesting) + return NBCON_PRIO_EMERGENCY; + + return NBCON_PRIO_NORMAL; +} + +/** + * nbcon_legacy_emit_next_record - Print one record for an nbcon console + * in legacy contexts + * @con: The console to print on + * @handover: Will be set to true if a printk waiter has taken over the + * console_lock, in which case the caller is no longer holding + * both the console_lock and the SRCU read lock. Otherwise it + * is set to false. + * @cookie: The cookie from the SRCU read lock. + * @use_atomic: Set true when called in an atomic or unknown context. + * It affects which nbcon callback will be used: write_atomic() + * or write_thread(). + * + * When false, the write_thread() callback is used and would be + * called in a preemtible context unless disabled by the + * device_lock. The legacy handover is not allowed in this mode. + * + * Context: Any context except NMI. + * Return: True, when a record has been printed and there are still + * pending records. The caller might want to continue flushing. + * + * False, when there is no pending record, or when the console + * context cannot be acquired, or the ownership has been lost. + * The caller should give up. Either the job is done, cannot be + * done, or will be handled by the owning context. + * + * This function is meant to be called by console_flush_all() to print records + * on nbcon consoles from legacy context (printing via console unlocking). + * Essentially it is the nbcon version of console_emit_next_record(). + */ +bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, + int cookie, bool use_atomic) +{ + struct nbcon_write_context wctxt = { }; + struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); + unsigned long flags; + bool progress; + + ctxt->console = con; + ctxt->prio = nbcon_get_default_prio(); + + if (use_atomic) { + /* + * In an atomic or unknown context, use the same procedure as + * in console_emit_next_record(). It allows to handover. + */ + printk_safe_enter_irqsave(flags); + console_lock_spinning_enable(); + stop_critical_timings(); + } + + progress = nbcon_emit_one(&wctxt, use_atomic); + + if (use_atomic) { + start_critical_timings(); + *handover = console_lock_spinning_disable_and_check(cookie); + printk_safe_exit_irqrestore(flags); } else { - con->pbufs = kmalloc(sizeof(*con->pbufs), GFP_KERNEL); - if (!con->pbufs) { - con_printk(KERN_ERR, con, "failed to allocate printing buffer\n"); - return false; + /* Non-atomic does not perform legacy spinning handovers. */ + *handover = false; + } + + return progress; +} + +/** + * __nbcon_atomic_flush_pending_con - Flush specified nbcon console using its + * write_atomic() callback + * @con: The nbcon console to flush + * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers + * + * Return: 0 if @con was flushed up to @stop_seq Otherwise, error code on + * failure. + * + * Errors: + * + * -EPERM: Unable to acquire console ownership. + * + * -EAGAIN: Another context took over ownership while printing. + * + * -ENOENT: A record before @stop_seq is not available. + * + * If flushing up to @stop_seq was not successful, it only makes sense for the + * caller to try again when -EAGAIN was returned. When -EPERM is returned, + * this context is not allowed to acquire the console. When -ENOENT is + * returned, it cannot be expected that the unfinalized record will become + * available. + */ +static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, + bool allow_unsafe_takeover) +{ + struct nbcon_write_context wctxt = { }; + struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt); + int err = 0; + + ctxt->console = con; + ctxt->spinwait_max_us = 2000; + ctxt->prio = nbcon_get_default_prio(); + ctxt->allow_unsafe_takeover = allow_unsafe_takeover; + + if (!nbcon_context_try_acquire(ctxt)) + return -EPERM; + + while (nbcon_seq_read(con) < stop_seq) { + /* + * nbcon_emit_next_record() returns false when the console was + * handed over or taken over. In both cases the context is no + * longer valid. + */ + if (!nbcon_emit_next_record(&wctxt, true)) + return -EAGAIN; + + if (!ctxt->backlog) { + /* Are there reserved but not yet finalized records? */ + if (nbcon_seq_read(con) < stop_seq) + err = -ENOENT; + break; } } - return true; + nbcon_context_release(ctxt); + return err; +} + +/** + * nbcon_atomic_flush_pending_con - Flush specified nbcon console using its + * write_atomic() callback + * @con: The nbcon console to flush + * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers + * + * This will stop flushing before @stop_seq if another context has ownership. + * That context is then responsible for the flushing. Likewise, if new records + * are added while this context was flushing and there is no other context + * to handle the printing, this context must also flush those records. + */ +static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, + bool allow_unsafe_takeover) +{ + struct console_flush_type ft; + unsigned long flags; + int err; + +again: + /* + * Atomic flushing does not use console driver synchronization (i.e. + * it does not hold the port lock for uart consoles). Therefore IRQs + * must be disabled to avoid being interrupted and then calling into + * a driver that will deadlock trying to acquire console ownership. + */ + local_irq_save(flags); + + err = __nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); + + local_irq_restore(flags); + + /* + * If there was a new owner (-EPERM, -EAGAIN), that context is + * responsible for completing. + * + * Do not wait for records not yet finalized (-ENOENT) to avoid a + * possible deadlock. They will either get flushed by the writer or + * eventually skipped on panic CPU. + */ + if (err) + return; + + /* + * If flushing was successful but more records are available, this + * context must flush those remaining records if the printer thread + * is not available do it. + */ + printk_get_console_flush_type(&ft); + if (!ft.nbcon_offload && + prb_read_valid(prb, nbcon_seq_read(con), NULL)) { + stop_seq = prb_next_reserve_seq(prb); + goto again; + } +} + +/** + * __nbcon_atomic_flush_pending - Flush all nbcon consoles using their + * write_atomic() callback + * @stop_seq: Flush up until this record + * @allow_unsafe_takeover: True, to allow unsafe hostile takeovers + */ +static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeover) +{ + struct console *con; + int cookie; + + cookie = console_srcu_read_lock(); + for_each_console_srcu(con) { + short flags = console_srcu_read_flags(con); + + if (!(flags & CON_NBCON)) + continue; + + if (!console_is_usable(con, flags, true)) + continue; + + if (nbcon_seq_read(con) >= stop_seq) + continue; + + nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover); + } + console_srcu_read_unlock(cookie); +} + +/** + * nbcon_atomic_flush_pending - Flush all nbcon consoles using their + * write_atomic() callback + * + * Flush the backlog up through the currently newest record. Any new + * records added while flushing will not be flushed if there is another + * context available to handle the flushing. This is to avoid one CPU + * printing unbounded because other CPUs continue to add records. + */ +void nbcon_atomic_flush_pending(void) +{ + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), false); +} + +/** + * nbcon_atomic_flush_unsafe - Flush all nbcon consoles using their + * write_atomic() callback and allowing unsafe hostile takeovers + * + * Flush the backlog up through the currently newest record. Unsafe hostile + * takeovers will be performed, if necessary. + */ +void nbcon_atomic_flush_unsafe(void) +{ + __nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), true); +} + +/** + * nbcon_cpu_emergency_enter - Enter an emergency section where printk() + * messages for that CPU are flushed directly + * + * Context: Any context. Disables preemption. + * + * When within an emergency section, printk() calls will attempt to flush any + * pending messages in the ringbuffer. + */ +void nbcon_cpu_emergency_enter(void) +{ + unsigned int *cpu_emergency_nesting; + + preempt_disable(); + + cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting(); + (*cpu_emergency_nesting)++; +} + +/** + * nbcon_cpu_emergency_exit - Exit an emergency section + * + * Context: Within an emergency section. Enables preemption. + */ +void nbcon_cpu_emergency_exit(void) +{ + unsigned int *cpu_emergency_nesting; + + cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting(); + + if (!WARN_ON_ONCE(*cpu_emergency_nesting == 0)) + (*cpu_emergency_nesting)--; + + preempt_enable(); } /** - * nbcon_init - Initialize the nbcon console specific data + * nbcon_alloc - Allocate and init the nbcon console specific data * @con: Console to initialize * - * nbcon_alloc() *must* be called and succeed before this function - * is called. + * Return: True if the console was fully allocated and initialized. + * Otherwise @con must not be registered. * - * This function expects that the legacy @con->seq has been set. + * When allocation and init was successful, the console must be properly + * freed using nbcon_free() once it is no longer needed. */ -void nbcon_init(struct console *con) +bool nbcon_alloc(struct console *con) { struct nbcon_state state = { }; - /* nbcon_alloc() must have been called and successful! */ - BUG_ON(!con->pbufs); + /* The write_thread() callback is mandatory. */ + if (WARN_ON(!con->write_thread)) + return false; - nbcon_seq_force(con, con->seq); + rcuwait_init(&con->rcuwait); + init_irq_work(&con->irq_work, nbcon_irq_work); + atomic_long_set(&ACCESS_PRIVATE(con, nbcon_prev_seq), -1UL); nbcon_state_set(con, &state); + + /* + * Initialize @nbcon_seq to the highest possible sequence number so + * that practically speaking it will have nothing to print until a + * desired initial sequence number has been set via nbcon_seq_force(). + */ + atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), ULSEQ_MAX(prb)); + + if (con->flags & CON_BOOT) { + /* + * Boot console printing is synchronized with legacy console + * printing, so boot consoles can share the same global printk + * buffers. + */ + con->pbufs = &printk_shared_pbufs; + } else { + con->pbufs = kmalloc(sizeof(*con->pbufs), GFP_KERNEL); + if (!con->pbufs) { + con_printk(KERN_ERR, con, "failed to allocate printing buffer\n"); + return false; + } + + if (printk_kthreads_running) { + if (!nbcon_kthread_create(con)) { + kfree(con->pbufs); + con->pbufs = NULL; + return false; + } + } + } + + return true; } /** @@ -986,6 +1721,9 @@ void nbcon_free(struct console *con) { struct nbcon_state state = { }; + if (printk_kthreads_running) + nbcon_kthread_stop(con); + nbcon_state_set(con, &state); /* Boot consoles share global printk buffers. */ @@ -994,3 +1732,85 @@ void nbcon_free(struct console *con) con->pbufs = NULL; } + +/** + * nbcon_device_try_acquire - Try to acquire nbcon console and enter unsafe + * section + * @con: The nbcon console to acquire + * + * Context: Under the locking mechanism implemented in + * @con->device_lock() including disabling migration. + * Return: True if the console was acquired. False otherwise. + * + * Console drivers will usually use their own internal synchronization + * mechasism to synchronize between console printing and non-printing + * activities (such as setting baud rates). However, nbcon console drivers + * supporting atomic consoles may also want to mark unsafe sections when + * performing non-printing activities in order to synchronize against their + * atomic_write() callback. + * + * This function acquires the nbcon console using priority NBCON_PRIO_NORMAL + * and marks it unsafe for handover/takeover. + */ +bool nbcon_device_try_acquire(struct console *con) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(con, nbcon_device_ctxt); + + cant_migrate(); + + memset(ctxt, 0, sizeof(*ctxt)); + ctxt->console = con; + ctxt->prio = NBCON_PRIO_NORMAL; + + if (!nbcon_context_try_acquire(ctxt)) + return false; + + if (!nbcon_context_enter_unsafe(ctxt)) + return false; + + return true; +} +EXPORT_SYMBOL_GPL(nbcon_device_try_acquire); + +/** + * nbcon_device_release - Exit unsafe section and release the nbcon console + * @con: The nbcon console acquired in nbcon_device_try_acquire() + */ +void nbcon_device_release(struct console *con) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(con, nbcon_device_ctxt); + struct console_flush_type ft; + int cookie; + + if (!nbcon_context_exit_unsafe(ctxt)) + return; + + nbcon_context_release(ctxt); + + /* + * This context must flush any new records added while the console + * was locked if the printer thread is not available to do it. The + * console_srcu_read_lock must be taken to ensure the console is + * usable throughout flushing. + */ + cookie = console_srcu_read_lock(); + printk_get_console_flush_type(&ft); + if (console_is_usable(con, console_srcu_read_flags(con), true) && + !ft.nbcon_offload && + prb_read_valid(prb, nbcon_seq_read(con), NULL)) { + /* + * If nbcon_atomic flushing is not available, fallback to + * using the legacy loop. + */ + if (ft.nbcon_atomic) { + __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false); + } else if (ft.legacy_direct) { + if (console_trylock()) + console_unlock(); + } else if (ft.legacy_offload) { + printk_trigger_flush(); + } + } + console_srcu_read_unlock(cookie); +} +EXPORT_SYMBOL_GPL(nbcon_device_release); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 6ff8d47e145f..71e4fe6f9b85 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -34,6 +34,7 @@ #include <linux/security.h> #include <linux/memblock.h> #include <linux/syscalls.h> +#include <linux/syscore_ops.h> #include <linux/vmcore_info.h> #include <linux/ratelimit.h> #include <linux/kmsg_dump.h> @@ -282,6 +283,7 @@ EXPORT_SYMBOL(console_list_unlock); * Return: A cookie to pass to console_srcu_read_unlock(). */ int console_srcu_read_lock(void) + __acquires(&console_srcu) { return srcu_read_lock_nmisafe(&console_srcu); } @@ -295,6 +297,7 @@ EXPORT_SYMBOL(console_srcu_read_lock); * Counterpart to console_srcu_read_lock() */ void console_srcu_read_unlock(int cookie) + __releases(&console_srcu) { srcu_read_unlock_nmisafe(&console_srcu, cookie); } @@ -461,14 +464,43 @@ static int console_msg_format = MSG_FORMAT_DEFAULT; /* syslog_lock protects syslog_* variables and write access to clear_seq. */ static DEFINE_MUTEX(syslog_lock); +/* + * Specifies if a legacy console is registered. If legacy consoles are + * present, it is necessary to perform the console lock/unlock dance + * whenever console flushing should occur. + */ +bool have_legacy_console; + +/* + * Specifies if an nbcon console is registered. If nbcon consoles are present, + * synchronous printing of legacy consoles will not occur during panic until + * the backtrace has been stored to the ringbuffer. + */ +bool have_nbcon_console; + +/* + * Specifies if a boot console is registered. If boot consoles are present, + * nbcon consoles cannot print simultaneously and must be synchronized by + * the console lock. This is because boot consoles and nbcon consoles may + * have mapped the same hardware. + */ +bool have_boot_console; + +/* See printk_legacy_allow_panic_sync() for details. */ +bool legacy_allow_panic_sync; + #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); +static DECLARE_WAIT_QUEUE_HEAD(legacy_wait); /* All 3 protected by @syslog_lock. */ /* the next printk record to read by syslog(READ) or /proc/kmsg */ static u64 syslog_seq; static size_t syslog_partial; static bool syslog_time; +/* True when _all_ printer threads are available for printing. */ +bool printk_kthreads_running; + struct latched_seq { seqcount_latch_t latch; u64 val[2]; @@ -1850,7 +1882,7 @@ static bool console_waiter; * there may be a waiter spinning (like a spinlock). Also it must be * ready to hand over the lock at the end of the section. */ -static void console_lock_spinning_enable(void) +void console_lock_spinning_enable(void) { /* * Do not use spinning in panic(). The panic CPU wants to keep the lock. @@ -1889,7 +1921,7 @@ lockdep: * * Return: 1 if the lock rights were passed, 0 otherwise. */ -static int console_lock_spinning_disable_and_check(int cookie) +int console_lock_spinning_disable_and_check(int cookie) { int waiter; @@ -2300,12 +2332,30 @@ out: return ret; } +/* + * This acts as a one-way switch to allow legacy consoles to print from + * the printk() caller context on a panic CPU. It also attempts to flush + * the legacy consoles in this context. + */ +void printk_legacy_allow_panic_sync(void) +{ + struct console_flush_type ft; + + legacy_allow_panic_sync = true; + + printk_get_console_flush_type(&ft); + if (ft.legacy_direct) { + if (console_trylock()) + console_unlock(); + } +} + asmlinkage int vprintk_emit(int facility, int level, const struct dev_printk_info *dev_info, const char *fmt, va_list args) { + struct console_flush_type ft; int printed_len; - bool in_sched = false; /* Suppress unimportant messages after panic happens */ if (unlikely(suppress_printk)) @@ -2319,17 +2369,26 @@ asmlinkage int vprintk_emit(int facility, int level, if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace) return 0; + printk_get_console_flush_type(&ft); + + /* If called from the scheduler, we can not call up(). */ if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; - in_sched = true; + ft.legacy_offload |= ft.legacy_direct; + ft.legacy_direct = false; } printk_delay(level); printed_len = vprintk_store(facility, level, dev_info, fmt, args); - /* If called from the scheduler, we can not call up(). */ - if (!in_sched) { + if (ft.nbcon_atomic) + nbcon_atomic_flush_pending(); + + if (ft.nbcon_offload) + nbcon_kthreads_wake(); + + if (ft.legacy_direct) { /* * The caller may be holding system-critical or * timing-sensitive locks. Disable preemption during @@ -2349,7 +2408,7 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } - if (in_sched) + if (ft.legacy_offload) defer_console_output(); else wake_up_klogd(); @@ -2678,6 +2737,7 @@ void suspend_console(void) void resume_console(void) { + struct console_flush_type ft; struct console *con; if (!console_suspend_enabled) @@ -2695,6 +2755,12 @@ void resume_console(void) */ synchronize_srcu(&console_srcu); + printk_get_console_flush_type(&ft); + if (ft.nbcon_offload) + nbcon_kthreads_wake(); + if (ft.legacy_offload) + defer_console_output(); + pr_flush(1000, true); } @@ -2709,10 +2775,16 @@ void resume_console(void) */ static int console_cpu_notify(unsigned int cpu) { + struct console_flush_type ft; + if (!cpuhp_tasks_frozen) { - /* If trylock fails, someone else is doing the printing */ - if (console_trylock()) - console_unlock(); + printk_get_console_flush_type(&ft); + if (ft.nbcon_atomic) + nbcon_atomic_flush_pending(); + if (ft.legacy_direct) { + if (console_trylock()) + console_unlock(); + } } return 0; } @@ -2766,36 +2838,6 @@ int is_console_locked(void) } EXPORT_SYMBOL(is_console_locked); -/* - * Check if the given console is currently capable and allowed to print - * records. - * - * Requires the console_srcu_read_lock. - */ -static inline bool console_is_usable(struct console *con) -{ - short flags = console_srcu_read_flags(con); - - if (!(flags & CON_ENABLED)) - return false; - - if ((flags & CON_SUSPENDED)) - return false; - - if (!con->write) - return false; - - /* - * Console drivers may assume that per-cpu resources have been - * allocated. So unless they're explicitly marked as being able to - * cope (CON_ANYTIME) don't call them until this CPU is officially up. - */ - if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME)) - return false; - - return true; -} - static void __console_unlock(void) { console_locked = 0; @@ -2805,30 +2847,31 @@ static void __console_unlock(void) #ifdef CONFIG_PRINTK /* - * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". This - * is achieved by shifting the existing message over and inserting the dropped - * message. + * Prepend the message in @pmsg->pbufs->outbuf. This is achieved by shifting + * the existing message over and inserting the scratchbuf message. * - * @pmsg is the printk message to prepend. - * - * @dropped is the dropped count to report in the dropped message. + * @pmsg is the original printk message. + * @fmt is the printf format of the message which will prepend the existing one. * - * If the message text in @pmsg->pbufs->outbuf does not have enough space for - * the dropped message, the message text will be sufficiently truncated. + * If there is not enough space in @pmsg->pbufs->outbuf, the existing + * message text will be sufficiently truncated. * * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated. */ -void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped) +__printf(2, 3) +static void console_prepend_message(struct printk_message *pmsg, const char *fmt, ...) { struct printk_buffers *pbufs = pmsg->pbufs; const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf); const size_t outbuf_sz = sizeof(pbufs->outbuf); char *scratchbuf = &pbufs->scratchbuf[0]; char *outbuf = &pbufs->outbuf[0]; + va_list args; size_t len; - len = scnprintf(scratchbuf, scratchbuf_sz, - "** %lu printk messages dropped **\n", dropped); + va_start(args, fmt); + len = vscnprintf(scratchbuf, scratchbuf_sz, fmt, args); + va_end(args); /* * Make sure outbuf is sufficiently large before prepending. @@ -2851,6 +2894,30 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped) } /* + * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". + * @pmsg->outbuf_len is updated appropriately. + * + * @pmsg is the printk message to prepend. + * + * @dropped is the dropped count to report in the dropped message. + */ +void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped) +{ + console_prepend_message(pmsg, "** %lu printk messages dropped **\n", dropped); +} + +/* + * Prepend the message in @pmsg->pbufs->outbuf with a "replay message". + * @pmsg->outbuf_len is updated appropriately. + * + * @pmsg is the printk message to prepend. + */ +void console_prepend_replay(struct printk_message *pmsg) +{ + console_prepend_message(pmsg, "** replaying previous printk message **\n"); +} + +/* * Read and format the specified record (or a later record if the specified * record is not available). * @@ -2916,6 +2983,34 @@ out: } /* + * Legacy console printing from printk() caller context does not respect + * raw_spinlock/spinlock nesting. For !PREEMPT_RT the lockdep warning is a + * false positive. For PREEMPT_RT the false positive condition does not + * occur. + * + * This map is used to temporarily establish LD_WAIT_SLEEP context for the + * console write() callback when legacy printing to avoid false positive + * lockdep complaints, thus allowing lockdep to continue to function for + * real issues. + */ +#ifdef CONFIG_PREEMPT_RT +static inline void printk_legacy_allow_spinlock_enter(void) { } +static inline void printk_legacy_allow_spinlock_exit(void) { } +#else +static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP); + +static inline void printk_legacy_allow_spinlock_enter(void) +{ + lock_map_acquire_try(&printk_legacy_map); +} + +static inline void printk_legacy_allow_spinlock_exit(void) +{ + lock_map_release(&printk_legacy_map); +} +#endif /* CONFIG_PREEMPT_RT */ + +/* * Used as the printk buffers for non-panic, serialized console printing. * This is for legacy (!CON_NBCON) as well as all boot (CON_BOOT) consoles. * Its usage requires the console_lock held. @@ -2964,31 +3059,46 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co con->dropped = 0; } - /* - * While actively printing out messages, if another printk() - * were to occur on another CPU, it may wait for this one to - * finish. This task can not be preempted if there is a - * waiter waiting to take over. - * - * Interrupts are disabled because the hand over to a waiter - * must not be interrupted until the hand over is completed - * (@console_waiter is cleared). - */ - printk_safe_enter_irqsave(flags); - console_lock_spinning_enable(); + /* Write everything out to the hardware. */ - /* Do not trace print latency. */ - stop_critical_timings(); + if (force_legacy_kthread() && !panic_in_progress()) { + /* + * With forced threading this function is in a task context + * (either legacy kthread or get_init_console_seq()). There + * is no need for concern about printk reentrance, handovers, + * or lockdep complaints. + */ - /* Write everything out to the hardware. */ - con->write(con, outbuf, pmsg.outbuf_len); + con->write(con, outbuf, pmsg.outbuf_len); + con->seq = pmsg.seq + 1; + } else { + /* + * While actively printing out messages, if another printk() + * were to occur on another CPU, it may wait for this one to + * finish. This task can not be preempted if there is a + * waiter waiting to take over. + * + * Interrupts are disabled because the hand over to a waiter + * must not be interrupted until the hand over is completed + * (@console_waiter is cleared). + */ + printk_safe_enter_irqsave(flags); + console_lock_spinning_enable(); - start_critical_timings(); + /* Do not trace print latency. */ + stop_critical_timings(); - con->seq = pmsg.seq + 1; + printk_legacy_allow_spinlock_enter(); + con->write(con, outbuf, pmsg.outbuf_len); + printk_legacy_allow_spinlock_exit(); - *handover = console_lock_spinning_disable_and_check(cookie); - printk_safe_exit_irqrestore(flags); + start_critical_timings(); + + con->seq = pmsg.seq + 1; + + *handover = console_lock_spinning_disable_and_check(cookie); + printk_safe_exit_irqrestore(flags); + } skip: return true; } @@ -3001,6 +3111,8 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co return false; } +static inline void printk_kthreads_check_locked(void) { } + #endif /* CONFIG_PRINTK */ /* @@ -3028,6 +3140,7 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co */ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover) { + struct console_flush_type ft; bool any_usable = false; struct console *con; bool any_progress; @@ -3039,15 +3152,34 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove do { any_progress = false; + printk_get_console_flush_type(&ft); + cookie = console_srcu_read_lock(); for_each_console_srcu(con) { + short flags = console_srcu_read_flags(con); + u64 printk_seq; bool progress; - if (!console_is_usable(con)) + /* + * console_flush_all() is only responsible for nbcon + * consoles when the nbcon consoles cannot print via + * their atomic or threaded flushing. + */ + if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload)) + continue; + + if (!console_is_usable(con, flags, !do_cond_resched)) continue; any_usable = true; - progress = console_emit_next_record(con, handover, cookie); + if (flags & CON_NBCON) { + progress = nbcon_legacy_emit_next_record(con, handover, cookie, + !do_cond_resched); + printk_seq = nbcon_seq_read(con); + } else { + progress = console_emit_next_record(con, handover, cookie); + printk_seq = con->seq; + } /* * If a handover has occurred, the SRCU read lock @@ -3057,8 +3189,8 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove return false; /* Track the next of the highest seq flushed. */ - if (con->seq > *next_seq) - *next_seq = con->seq; + if (printk_seq > *next_seq) + *next_seq = printk_seq; if (!progress) continue; @@ -3081,19 +3213,7 @@ abandon: return false; } -/** - * console_unlock - unblock the console subsystem from printing - * - * Releases the console_lock which the caller holds to block printing of - * the console subsystem. - * - * While the console_lock was held, console output may have been buffered - * by printk(). If this is the case, console_unlock(); emits - * the output prior to releasing the lock. - * - * console_unlock(); may be called from any context. - */ -void console_unlock(void) +static void __console_flush_and_unlock(void) { bool do_cond_resched; bool handover; @@ -3137,6 +3257,29 @@ void console_unlock(void) */ } while (prb_read_valid(prb, next_seq, NULL) && console_trylock()); } + +/** + * console_unlock - unblock the legacy console subsystem from printing + * + * Releases the console_lock which the caller holds to block printing of + * the legacy console subsystem. + * + * While the console_lock was held, console output may have been buffered + * by printk(). If this is the case, console_unlock() emits the output on + * legacy consoles prior to releasing the lock. + * + * console_unlock(); may be called from any context. + */ +void console_unlock(void) +{ + struct console_flush_type ft; + + printk_get_console_flush_type(&ft); + if (ft.legacy_direct) + __console_flush_and_unlock(); + else + __console_unlock(); +} EXPORT_SYMBOL(console_unlock); /** @@ -3259,6 +3402,7 @@ static void __console_rewind_all(void) */ void console_flush_on_panic(enum con_flush_mode mode) { + struct console_flush_type ft; bool handover; u64 next_seq; @@ -3282,7 +3426,13 @@ void console_flush_on_panic(enum con_flush_mode mode) if (mode == CONSOLE_REPLAY_ALL) __console_rewind_all(); - console_flush_all(false, &next_seq, &handover); + printk_get_console_flush_type(&ft); + if (ft.nbcon_atomic) + nbcon_atomic_flush_pending(); + + /* Flush legacy consoles once allowed, even when dangerous. */ + if (legacy_allow_panic_sync) + console_flush_all(false, &next_seq, &handover); } /* @@ -3339,13 +3489,236 @@ EXPORT_SYMBOL(console_stop); void console_start(struct console *console) { + struct console_flush_type ft; + bool is_nbcon; + console_list_lock(); console_srcu_write_flags(console, console->flags | CON_ENABLED); + is_nbcon = console->flags & CON_NBCON; console_list_unlock(); + + /* + * Ensure that all SRCU list walks have completed. The related + * printing context must be able to see it is enabled so that + * it is guaranteed to wake up and resume printing. + */ + synchronize_srcu(&console_srcu); + + printk_get_console_flush_type(&ft); + if (is_nbcon && ft.nbcon_offload) + nbcon_kthread_wake(console); + else if (ft.legacy_offload) + defer_console_output(); + __pr_flush(console, 1000, true); } EXPORT_SYMBOL(console_start); +#ifdef CONFIG_PRINTK +static int unregister_console_locked(struct console *console); + +/* True when system boot is far enough to create printer threads. */ +static bool printk_kthreads_ready __ro_after_init; + +static struct task_struct *printk_legacy_kthread; + +static bool legacy_kthread_should_wakeup(void) +{ + struct console_flush_type ft; + struct console *con; + bool ret = false; + int cookie; + + if (kthread_should_stop()) + return true; + + printk_get_console_flush_type(&ft); + + cookie = console_srcu_read_lock(); + for_each_console_srcu(con) { + short flags = console_srcu_read_flags(con); + u64 printk_seq; + + /* + * The legacy printer thread is only responsible for nbcon + * consoles when the nbcon consoles cannot print via their + * atomic or threaded flushing. + */ + if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload)) + continue; + + if (!console_is_usable(con, flags, false)) + continue; + + if (flags & CON_NBCON) { + printk_seq = nbcon_seq_read(con); + } else { + /* + * It is safe to read @seq because only this + * thread context updates @seq. + */ + printk_seq = con->seq; + } + + if (prb_read_valid(prb, printk_seq, NULL)) { + ret = true; + break; + } + } + console_srcu_read_unlock(cookie); + + return ret; +} + +static int legacy_kthread_func(void *unused) +{ + for (;;) { + wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup()); + + if (kthread_should_stop()) + break; + + console_lock(); + __console_flush_and_unlock(); + } + + return 0; +} + +static bool legacy_kthread_create(void) +{ + struct task_struct *kt; + + lockdep_assert_console_list_lock_held(); + + kt = kthread_run(legacy_kthread_func, NULL, "pr/legacy"); + if (WARN_ON(IS_ERR(kt))) { + pr_err("failed to start legacy printing thread\n"); + return false; + } + + printk_legacy_kthread = kt; + + /* + * It is important that console printing threads are scheduled + * shortly after a printk call and with generous runtime budgets. + */ + sched_set_normal(printk_legacy_kthread, -20); + + return true; +} + +/** + * printk_kthreads_shutdown - shutdown all threaded printers + * + * On system shutdown all threaded printers are stopped. This allows printk + * to transition back to atomic printing, thus providing a robust mechanism + * for the final shutdown/reboot messages to be output. + */ +static void printk_kthreads_shutdown(void) +{ + struct console *con; + + console_list_lock(); + if (printk_kthreads_running) { + printk_kthreads_running = false; + + for_each_console(con) { + if (con->flags & CON_NBCON) + nbcon_kthread_stop(con); + } + + /* + * The threads may have been stopped while printing a + * backlog. Flush any records left over. + */ + nbcon_atomic_flush_pending(); + } + console_list_unlock(); +} + +static struct syscore_ops printk_syscore_ops = { + .shutdown = printk_kthreads_shutdown, +}; + +/* + * If appropriate, start nbcon kthreads and set @printk_kthreads_running. + * If any kthreads fail to start, those consoles are unregistered. + * + * Must be called under console_list_lock(). + */ +static void printk_kthreads_check_locked(void) +{ + struct hlist_node *tmp; + struct console *con; + + lockdep_assert_console_list_lock_held(); + + if (!printk_kthreads_ready) + return; + + if (have_legacy_console || have_boot_console) { + if (!printk_legacy_kthread && + force_legacy_kthread() && + !legacy_kthread_create()) { + /* + * All legacy consoles must be unregistered. If there + * are any nbcon consoles, they will set up their own + * kthread. + */ + hlist_for_each_entry_safe(con, tmp, &console_list, node) { + if (con->flags & CON_NBCON) + continue; + + unregister_console_locked(con); + } + } + } else if (printk_legacy_kthread) { + kthread_stop(printk_legacy_kthread); + printk_legacy_kthread = NULL; + } + + /* + * Printer threads cannot be started as long as any boot console is + * registered because there is no way to synchronize the hardware + * registers between boot console code and regular console code. + * It can only be known that there will be no new boot consoles when + * an nbcon console is registered. + */ + if (have_boot_console || !have_nbcon_console) { + /* Clear flag in case all nbcon consoles unregistered. */ + printk_kthreads_running = false; + return; + } + + if (printk_kthreads_running) + return; + + hlist_for_each_entry_safe(con, tmp, &console_list, node) { + if (!(con->flags & CON_NBCON)) + continue; + + if (!nbcon_kthread_create(con)) + unregister_console_locked(con); + } + + printk_kthreads_running = true; +} + +static int __init printk_set_kthreads_ready(void) +{ + register_syscore_ops(&printk_syscore_ops); + + console_list_lock(); + printk_kthreads_ready = true; + printk_kthreads_check_locked(); + console_list_unlock(); + + return 0; +} +early_initcall(printk_set_kthreads_ready); +#endif /* CONFIG_PRINTK */ + static int __read_mostly keep_bootcon; static int __init keep_bootcon_setup(char *str) @@ -3447,19 +3820,21 @@ static void try_enable_default_console(struct console *newcon) newcon->flags |= CON_CONSDEV; } -static void console_init_seq(struct console *newcon, bool bootcon_registered) +/* Return the starting sequence number for a newly registered console. */ +static u64 get_init_console_seq(struct console *newcon, bool bootcon_registered) { struct console *con; bool handover; + u64 init_seq; if (newcon->flags & (CON_PRINTBUFFER | CON_BOOT)) { /* Get a consistent copy of @syslog_seq. */ mutex_lock(&syslog_lock); - newcon->seq = syslog_seq; + init_seq = syslog_seq; mutex_unlock(&syslog_lock); } else { /* Begin with next message added to ringbuffer. */ - newcon->seq = prb_next_seq(prb); + init_seq = prb_next_seq(prb); /* * If any enabled boot consoles are due to be unregistered @@ -3480,7 +3855,7 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered) * Flush all consoles and set the console to start at * the next unprinted sequence number. */ - if (!console_flush_all(true, &newcon->seq, &handover)) { + if (!console_flush_all(true, &init_seq, &handover)) { /* * Flushing failed. Just choose the lowest * sequence of the enabled boot consoles. @@ -3493,19 +3868,30 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered) if (handover) console_lock(); - newcon->seq = prb_next_seq(prb); + init_seq = prb_next_seq(prb); for_each_console(con) { - if ((con->flags & CON_BOOT) && - (con->flags & CON_ENABLED) && - con->seq < newcon->seq) { - newcon->seq = con->seq; + u64 seq; + + if (!(con->flags & CON_BOOT) || + !(con->flags & CON_ENABLED)) { + continue; } + + if (con->flags & CON_NBCON) + seq = nbcon_seq_read(con); + else + seq = con->seq; + + if (seq < init_seq) + init_seq = seq; } } console_unlock(); } } + + return init_seq; } #define console_first() \ @@ -3534,9 +3920,12 @@ static int unregister_console_locked(struct console *console); */ void register_console(struct console *newcon) { - struct console *con; + bool use_device_lock = (newcon->flags & CON_NBCON) && newcon->write_atomic; bool bootcon_registered = false; bool realcon_registered = false; + struct console *con; + unsigned long flags; + u64 init_seq; int err; console_list_lock(); @@ -3614,10 +4003,31 @@ void register_console(struct console *newcon) } newcon->dropped = 0; - console_init_seq(newcon, bootcon_registered); + init_seq = get_init_console_seq(newcon, bootcon_registered); + + if (newcon->flags & CON_NBCON) { + have_nbcon_console = true; + nbcon_seq_force(newcon, init_seq); + } else { + have_legacy_console = true; + newcon->seq = init_seq; + } + + if (newcon->flags & CON_BOOT) + have_boot_console = true; - if (newcon->flags & CON_NBCON) - nbcon_init(newcon); + /* + * If another context is actively using the hardware of this new + * console, it will not be aware of the nbcon synchronization. This + * is a risk that two contexts could access the hardware + * simultaneously if this new console is used for atomic printing + * and the other context is still using the hardware. + * + * Use the driver synchronization to ensure that the hardware is not + * in use while this new console transitions to being registered. + */ + if (use_device_lock) + newcon->device_lock(newcon, &flags); /* * Put this console in the list - keep the @@ -3643,6 +4053,10 @@ void register_console(struct console *newcon) * register_console() completes. */ + /* This new console is now registered. */ + if (use_device_lock) + newcon->device_unlock(newcon, flags); + console_sysfs_notify(); /* @@ -3663,6 +4077,9 @@ void register_console(struct console *newcon) unregister_console_locked(con); } } + + /* Changed console list, may require printer threads to start/stop. */ + printk_kthreads_check_locked(); unlock: console_list_unlock(); } @@ -3671,6 +4088,12 @@ EXPORT_SYMBOL(register_console); /* Must be called under console_list_lock(). */ static int unregister_console_locked(struct console *console) { + bool use_device_lock = (console->flags & CON_NBCON) && console->write_atomic; + bool found_legacy_con = false; + bool found_nbcon_con = false; + bool found_boot_con = false; + unsigned long flags; + struct console *c; int res; lockdep_assert_console_list_lock_held(); @@ -3683,14 +4106,29 @@ static int unregister_console_locked(struct console *console) if (res > 0) return 0; + if (!console_is_registered_locked(console)) + res = -ENODEV; + else if (console_is_usable(console, console->flags, true)) + __pr_flush(console, 1000, true); + /* Disable it unconditionally */ console_srcu_write_flags(console, console->flags & ~CON_ENABLED); - if (!console_is_registered_locked(console)) - return -ENODEV; + if (res < 0) + return res; + + /* + * Use the driver synchronization to ensure that the hardware is not + * in use while this console transitions to being unregistered. + */ + if (use_device_lock) + console->device_lock(console, &flags); hlist_del_init_rcu(&console->node); + if (use_device_lock) + console->device_unlock(console, flags); + /* * <HISTORICAL> * If this isn't the last console and it has CON_CONSDEV set, we @@ -3718,6 +4156,29 @@ static int unregister_console_locked(struct console *console) if (console->exit) res = console->exit(console); + /* + * With this console gone, the global flags tracking registered + * console types may have changed. Update them. + */ + for_each_console(c) { + if (c->flags & CON_BOOT) + found_boot_con = true; + + if (c->flags & CON_NBCON) + found_nbcon_con = true; + else + found_legacy_con = true; + } + if (!found_boot_con) + have_boot_console = found_boot_con; + if (!found_legacy_con) + have_legacy_console = found_legacy_con; + if (!found_nbcon_con) + have_nbcon_console = found_nbcon_con; + + /* Changed console list, may require printer threads to start/stop. */ + printk_kthreads_check_locked(); + return res; } @@ -3864,6 +4325,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre { unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms); unsigned long remaining_jiffies = timeout_jiffies; + struct console_flush_type ft; struct console *c; u64 last_diff = 0; u64 printk_seq; @@ -3872,13 +4334,22 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre u64 diff; u64 seq; + /* Sorry, pr_flush() will not work this early. */ + if (system_state < SYSTEM_SCHEDULING) + return false; + might_sleep(); seq = prb_next_reserve_seq(prb); /* Flush the consoles so that records up to @seq are printed. */ - console_lock(); - console_unlock(); + printk_get_console_flush_type(&ft); + if (ft.nbcon_atomic) + nbcon_atomic_flush_pending(); + if (ft.legacy_direct) { + console_lock(); + console_unlock(); + } for (;;) { unsigned long begin_jiffies; @@ -3891,6 +4362,12 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre * console->seq. Releasing console_lock flushes more * records in case @seq is still not printed on all * usable consoles. + * + * Holding the console_lock is not necessary if there + * are no legacy or boot consoles. However, such a + * console could register at any time. Always hold the + * console_lock as a precaution rather than + * synchronizing against register_console(). */ console_lock(); @@ -3906,8 +4383,10 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre * that they make forward progress, so only increment * @diff for usable consoles. */ - if (!console_is_usable(c)) + if (!console_is_usable(c, flags, true) && + !console_is_usable(c, flags, false)) { continue; + } if (flags & CON_NBCON) { printk_seq = nbcon_seq_read(c); @@ -3975,9 +4454,13 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work) int pending = this_cpu_xchg(printk_pending, 0); if (pending & PRINTK_PENDING_OUTPUT) { - /* If trylock fails, someone else is doing the printing */ - if (console_trylock()) - console_unlock(); + if (force_legacy_kthread()) { + if (printk_legacy_kthread) + wake_up_interruptible(&legacy_wait); + } else { + if (console_trylock()) + console_unlock(); + } } if (pending & PRINTK_PENDING_WAKEUP) @@ -4383,8 +4866,17 @@ EXPORT_SYMBOL_GPL(kmsg_dump_rewind); */ void console_try_replay_all(void) { + struct console_flush_type ft; + + printk_get_console_flush_type(&ft); if (console_trylock()) { __console_rewind_all(); + if (ft.nbcon_atomic) + nbcon_atomic_flush_pending(); + if (ft.nbcon_offload) + nbcon_kthreads_wake(); + if (ft.legacy_offload) + defer_console_output(); /* Consoles are flushed as part of console_unlock(). */ console_unlock(); } diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h index 52626d0f1fa3..4ef81349d9fb 100644 --- a/kernel/printk/printk_ringbuffer.h +++ b/kernel/printk/printk_ringbuffer.h @@ -4,7 +4,10 @@ #define _KERNEL_PRINTK_RINGBUFFER_H #include <linux/atomic.h> +#include <linux/bits.h> #include <linux/dev_printk.h> +#include <linux/stddef.h> +#include <linux/types.h> /* * Meta information about each stored message. @@ -120,7 +123,7 @@ enum desc_state { #define _DATA_SIZE(sz_bits) (1UL << (sz_bits)) #define _DESCS_COUNT(ct_bits) (1U << (ct_bits)) -#define DESC_SV_BITS (sizeof(unsigned long) * 8) +#define DESC_SV_BITS BITS_PER_LONG #define DESC_FLAGS_SHIFT (DESC_SV_BITS - 2) #define DESC_FLAGS_MASK (3UL << DESC_FLAGS_SHIFT) #define DESC_STATE(sv) (3UL & (sv >> DESC_FLAGS_SHIFT)) @@ -401,10 +404,12 @@ u64 prb_next_reserve_seq(struct printk_ringbuffer *rb); #define __u64seq_to_ulseq(u64seq) (u64seq) #define __ulseq_to_u64seq(rb, ulseq) (ulseq) +#define ULSEQ_MAX(rb) (-1) #else /* CONFIG_64BIT */ #define __u64seq_to_ulseq(u64seq) ((u32)u64seq) +#define ULSEQ_MAX(rb) __u64seq_to_ulseq(prb_first_seq(rb) + 0x80000000UL) static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq) { diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 6d10927a07d8..2b35a9d3919d 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -26,6 +26,29 @@ void __printk_safe_exit(void) this_cpu_dec(printk_context); } +void __printk_deferred_enter(void) +{ + cant_migrate(); + __printk_safe_enter(); +} + +void __printk_deferred_exit(void) +{ + cant_migrate(); + __printk_safe_exit(); +} + +bool is_printk_legacy_deferred(void) +{ + /* + * The per-CPU variable @printk_context can be read safely in any + * context. CPU migration is always disabled when set. + */ + return (force_legacy_kthread() || + this_cpu_read(printk_context) || + in_nmi()); +} + asmlinkage int vprintk(const char *fmt, va_list args) { #ifdef CONFIG_KGDB_KDB @@ -38,7 +61,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) * Use the main logbuf even in NMI. But avoid calling console * drivers that might have their own locks. */ - if (this_cpu_read(printk_context) || in_nmi()) + if (is_printk_legacy_deferred()) return vprintk_deferred(fmt, args); /* No obstacles. */ diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 4acd29d16fdb..f6b35a0585a8 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -7,6 +7,7 @@ * Authors: Paul E. McKenney <paulmck@linux.ibm.com> */ +#include <linux/console.h> #include <linux/lockdep.h> static void rcu_exp_handler(void *unused); @@ -590,6 +591,9 @@ static void synchronize_rcu_expedited_wait(void) return; if (rcu_stall_is_suppressed()) continue; + + nbcon_cpu_emergency_enter(); + j = jiffies; rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start)); trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall")); @@ -643,6 +647,9 @@ static void synchronize_rcu_expedited_wait(void) rcu_exp_print_detail_task_stall_rnp(rnp); } jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3; + + nbcon_cpu_emergency_exit(); + panic_on_rcu_stall(); } } diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 4b0e9d7c4c68..b3a6943127bc 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -7,6 +7,7 @@ * Author: Paul E. McKenney <paulmck@linux.ibm.com> */ +#include <linux/console.h> #include <linux/kvm_para.h> #include <linux/rcu_notifier.h> @@ -605,6 +606,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) if (rcu_stall_is_suppressed()) return; + nbcon_cpu_emergency_enter(); + /* * OK, time to rat on our buddy... * See Documentation/RCU/stallwarn.rst for info on how to debug @@ -657,6 +660,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation(); + nbcon_cpu_emergency_exit(); + panic_on_rcu_stall(); rcu_force_quiescent_state(); /* Kick them all. */ @@ -677,6 +682,8 @@ static void print_cpu_stall(unsigned long gps) if (rcu_stall_is_suppressed()) return; + nbcon_cpu_emergency_enter(); + /* * OK, time to rat on ourselves... * See Documentation/RCU/stallwarn.rst for info on how to debug @@ -706,6 +713,8 @@ static void print_cpu_stall(unsigned long gps) jiffies + 3 * rcu_jiffies_till_stall_check() + 3); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + nbcon_cpu_emergency_exit(); + panic_on_rcu_stall(); /* |