diff options
Diffstat (limited to 'kernel/rcutree.c')
| -rw-r--r-- | kernel/rcutree.c | 135 |
1 files changed, 101 insertions, 34 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 7387e46009d9..af0dc3472a4b 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -322,16 +322,17 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) } /* - * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle + * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state * * If the new value of the ->dynticks_nesting counter now is zero, * we really have entered idle, and must do the appropriate accounting. * The caller must have disabled interrupts. */ -static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval) +static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval, + bool user) { trace_rcu_dyntick("Start", oldval, 0); - if (!is_idle_task(current)) { + if (!is_idle_task(current) && !user) { struct task_struct *idle = idle_task(smp_processor_id()); trace_rcu_dyntick("Error on entry: not idle task", oldval, 0); @@ -348,7 +349,7 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval) WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); /* - * The idle task is not permitted to enter the idle loop while + * It is illegal to enter an extended quiescent state while * in an RCU read-side critical section. */ rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), @@ -359,19 +360,11 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval) "Illegal idle entry in RCU-sched read-side critical section."); } -/** - * rcu_idle_enter - inform RCU that current CPU is entering idle - * - * Enter idle mode, in other words, -leave- the mode in which RCU - * read-side critical sections can occur. (Though RCU read-side - * critical sections can occur in irq handlers in idle, a possibility - * handled by irq_enter() and irq_exit().) - * - * We crowbar the ->dynticks_nesting field to zero to allow for - * the possibility of usermode upcalls having messed up our count - * of interrupt nesting level during the prior busy period. +/* + * Enter an RCU extended quiescent state, which can be either the + * idle loop or adaptive-tickless usermode execution. */ -void rcu_idle_enter(void) +static void rcu_eqs_enter(bool user) { unsigned long flags; long long oldval; @@ -385,12 +378,54 @@ void rcu_idle_enter(void) rdtp->dynticks_nesting = 0; else rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; - rcu_idle_enter_common(rdtp, oldval); + rcu_eqs_enter_common(rdtp, oldval, user); local_irq_restore(flags); } + +/** + * rcu_idle_enter - inform RCU that current CPU is entering idle + * + * Enter idle mode, in other words, -leave- the mode in which RCU + * read-side critical sections can occur. (Though RCU read-side + * critical sections can occur in irq handlers in idle, a possibility + * handled by irq_enter() and irq_exit().) + * + * We crowbar the ->dynticks_nesting field to zero to allow for + * the possibility of usermode upcalls having messed up our count + * of interrupt nesting level during the prior busy period. + */ +void rcu_idle_enter(void) +{ + rcu_eqs_enter(0); +} EXPORT_SYMBOL_GPL(rcu_idle_enter); /** + * rcu_user_enter - inform RCU that we are resuming userspace. + * + * Enter RCU idle mode right before resuming userspace. No use of RCU + * is permitted between this call and rcu_user_exit(). This way the + * CPU doesn't need to maintain the tick for RCU maintenance purposes + * when the CPU runs in userspace. + */ +void rcu_user_enter(void) +{ + /* + * Some contexts may involve an exception occuring in an irq, + * leading to that nesting: + * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() + * This would mess up the dyntick_nesting count though. And rcu_irq_*() + * helpers are enough to protect RCU uses inside the exception. So + * just return immediately if we detect we are in an IRQ. + */ + if (in_interrupt()) + return; + + rcu_eqs_enter(1); +} + + +/** * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle * * Exit from an interrupt handler, which might possibly result in entering @@ -420,18 +455,19 @@ void rcu_irq_exit(void) if (rdtp->dynticks_nesting) trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting); else - rcu_idle_enter_common(rdtp, oldval); + rcu_eqs_enter_common(rdtp, oldval, 1); local_irq_restore(flags); } /* - * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle + * rcu_eqs_exit_common - current CPU moving away from extended quiescent state * * If the new value of the ->dynticks_nesting counter was previously zero, * we really have exited idle, and must do the appropriate accounting. * The caller must have disabled interrupts. */ -static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) +static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval, + int user) { smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */ atomic_inc(&rdtp->dynticks); @@ -440,7 +476,7 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); rcu_cleanup_after_idle(smp_processor_id()); trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting); - if (!is_idle_task(current)) { + if (!is_idle_task(current) && !user) { struct task_struct *idle = idle_task(smp_processor_id()); trace_rcu_dyntick("Error on exit: not idle task", @@ -452,18 +488,11 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) } } -/** - * rcu_idle_exit - inform RCU that current CPU is leaving idle - * - * Exit idle mode, in other words, -enter- the mode in which RCU - * read-side critical sections can occur. - * - * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to - * allow for the possibility of usermode upcalls messing up our count - * of interrupt nesting level during the busy period that is just - * now starting. +/* + * Exit an RCU extended quiescent state, which can be either the + * idle loop or adaptive-tickless usermode execution. */ -void rcu_idle_exit(void) +static void rcu_eqs_exit(bool user) { unsigned long flags; struct rcu_dynticks *rdtp; @@ -477,12 +506,50 @@ void rcu_idle_exit(void) rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; else rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; - rcu_idle_exit_common(rdtp, oldval); + rcu_eqs_exit_common(rdtp, oldval, user); local_irq_restore(flags); } + +/** + * rcu_idle_exit - inform RCU that current CPU is leaving idle + * + * Exit idle mode, in other words, -enter- the mode in which RCU + * read-side critical sections can occur. + * + * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to + * allow for the possibility of usermode upcalls messing up our count + * of interrupt nesting level during the busy period that is just + * now starting. + */ +void rcu_idle_exit(void) +{ + rcu_eqs_exit(0); +} EXPORT_SYMBOL_GPL(rcu_idle_exit); /** + * rcu_user_exit - inform RCU that we are exiting userspace. + * + * Exit RCU idle mode while entering the kernel because it can + * run a RCU read side critical section anytime. + */ +void rcu_user_exit(void) +{ + /* + * Some contexts may involve an exception occuring in an irq, + * leading to that nesting: + * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() + * This would mess up the dyntick_nesting count though. And rcu_irq_*() + * helpers are enough to protect RCU uses inside the exception. So + * just return immediately if we detect we are in an IRQ. + */ + if (in_interrupt()) + return; + + rcu_eqs_exit(1); +} + +/** * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle * * Enter an interrupt handler, which might possibly result in exiting @@ -515,7 +582,7 @@ void rcu_irq_enter(void) if (oldval) trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting); else - rcu_idle_exit_common(rdtp, oldval); + rcu_eqs_exit_common(rdtp, oldval, 1); local_irq_restore(flags); } |