3 files changed, 54 insertions, 19 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index a91bdf802967..48a24e7b309d 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -64,6 +64,7 @@ struct dev_printk_info;
 
 extern struct printk_ringbuffer *prb;
 extern bool printk_kthreads_running;
+extern bool debug_non_panic_cpus;
 
 __printf(4, 0)
 int vprintk_store(int facility, int level,
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 07668433644b..1eea80d0648e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2375,6 +2375,22 @@ void printk_legacy_allow_panic_sync(void)
 	}
 }
 
+bool __read_mostly debug_non_panic_cpus;
+
+#ifdef CONFIG_PRINTK_CALLER
+static int __init debug_non_panic_cpus_setup(char *str)
+{
+	debug_non_panic_cpus = true;
+	pr_info("allow messages from non-panic CPUs in panic()\n");
+
+	return 0;
+}
+early_param("debug_non_panic_cpus", debug_non_panic_cpus_setup);
+module_param(debug_non_panic_cpus, bool, 0644);
+MODULE_PARM_DESC(debug_non_panic_cpus,
+		 "allow messages from non-panic CPUs in panic()");
+#endif
+
 asmlinkage int vprintk_emit(int facility, int level,
 			    const struct dev_printk_info *dev_info,
 			    const char *fmt, va_list args)
@@ -2391,7 +2407,9 @@ asmlinkage int vprintk_emit(int facility, int level,
 	 * non-panic CPUs are generating any messages, they will be
 	 * silently dropped.
 	 */
-	if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace)
+	if (other_cpu_in_panic() &&
+	    !debug_non_panic_cpus &&
+	    !panic_triggering_all_cpu_backtrace)
 		return 0;
 
 	printk_get_console_flush_type(&ft);
@@ -2461,7 +2479,6 @@ asmlinkage __visible int _printk(const char *fmt, ...)
 }
 EXPORT_SYMBOL(_printk);
 
-static bool pr_flush(int timeout_ms, bool reset_on_progress);
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
 
 #else /* CONFIG_PRINTK */
@@ -2474,7 +2491,6 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
 
 static u64 syslog_seq;
 
-static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
 
 #endif /* CONFIG_PRINTK */
@@ -2733,11 +2749,11 @@ module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool
 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
 
 /**
- * suspend_console - suspend the console subsystem
+ * console_suspend_all - suspend the console subsystem
  *
  * This disables printk() while we go into suspend states
  */
-void suspend_console(void)
+void console_suspend_all(void)
 {
 	struct console *con;
 
@@ -2760,7 +2776,7 @@ void suspend_console(void)
 	synchronize_srcu(&console_srcu);
 }
 
-void resume_console(void)
+void console_resume_all(void)
 {
 	struct console_flush_type ft;
 	struct console *con;
@@ -3342,7 +3358,12 @@ void console_unblank(void)
 	 */
 	cookie = console_srcu_read_lock();
 	for_each_console_srcu(c) {
-		if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) {
+		short flags = console_srcu_read_flags(c);
+
+		if (flags & CON_SUSPENDED)
+			continue;
+
+		if ((flags & CON_ENABLED) && c->unblank) {
 			found_unblank = true;
 			break;
 		}
@@ -3379,7 +3400,12 @@ void console_unblank(void)
 
 	cookie = console_srcu_read_lock();
 	for_each_console_srcu(c) {
-		if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank)
+		short flags = console_srcu_read_flags(c);
+
+		if (flags & CON_SUSPENDED)
+			continue;
+
+		if ((flags & CON_ENABLED) && c->unblank)
 			c->unblank();
 	}
 	console_srcu_read_unlock(cookie);
@@ -3497,10 +3523,10 @@ struct tty_driver *console_device(int *index)
 
 /*
  * Prevent further output on the passed console device so that (for example)
- * serial drivers can disable console output before suspending a port, and can
+ * serial drivers can suspend console output before suspending a port, and can
  * re-enable output afterwards.
  */
-void console_stop(struct console *console)
+void console_suspend(struct console *console)
 {
 	__pr_flush(console, 1000, true);
 	console_list_lock();
@@ -3515,9 +3541,9 @@ void console_stop(struct console *console)
 	 */
 	synchronize_srcu(&console_srcu);
 }
-EXPORT_SYMBOL(console_stop);
+EXPORT_SYMBOL(console_suspend);
 
-void console_start(struct console *console)
+void console_resume(struct console *console)
 {
 	struct console_flush_type ft;
 	bool is_nbcon;
@@ -3542,7 +3568,7 @@ void console_start(struct console *console)
 
 	__pr_flush(console, 1000, true);
 }
-EXPORT_SYMBOL(console_start);
+EXPORT_SYMBOL(console_resume);
 
 #ifdef CONFIG_PRINTK
 static int unregister_console_locked(struct console *console);
@@ -4277,6 +4303,11 @@ void __init console_init(void)
 	initcall_t call;
 	initcall_entry_t *ce;
 
+#ifdef CONFIG_NULL_TTY_DEFAULT_CONSOLE
+	if (!console_set_on_cmdline)
+		add_preferred_console("ttynull", 0, NULL);
+#endif
+
 	/* Setup the default TTY line discipline. */
 	n_tty_init();
 
@@ -4466,7 +4497,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
  * Context: Process context. May sleep while acquiring console lock.
  * Return: true if all usable printers are caught up.
  */
-static bool pr_flush(int timeout_ms, bool reset_on_progress)
+bool pr_flush(int timeout_ms, bool reset_on_progress)
 {
 	return __pr_flush(NULL, timeout_ms, reset_on_progress);
 }
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index 88e8f3a61922..d9fb053cff67 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -2133,9 +2133,9 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
 			 * there may be other finalized records beyond that
 			 * need to be printed for a panic situation. If this
 			 * is the panic CPU, skip this
-			 * non-existent/non-finalized record unless it is
-			 * at or beyond the head, in which case it is not
-			 * possible to continue.
+			 * non-existent/non-finalized record unless non-panic
+			 * CPUs are still running and their debugging is
+			 * explicitly enabled.
 			 *
 			 * Note that new messages printed on panic CPU are
 			 * finalized when we are here. The only exception
@@ -2143,10 +2143,13 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
 			 * But it would have the sequence number returned
 			 * by "prb_next_reserve_seq() - 1".
 			 */
-			if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb)))
+			if (this_cpu_in_panic() &&
+			    (!debug_non_panic_cpus || legacy_allow_panic_sync) &&
+			    ((*seq + 1) < prb_next_reserve_seq(rb))) {
 				(*seq)++;
-			else
+			} else {
 				return false;
+			}
 		}
 	}