6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: John Ogness john.ogness@linutronix.de
[ Upstream commit 51a1d258e50e03a0216bf42b6af9ff34ec402ac1 ]
When in a panic situation, non-panic CPUs should avoid holding the console lock so as not to contend with the panic CPU. This is already implemented with abandon_console_lock_in_panic(), which is checked after each printed line. However, non-panic CPUs should also avoid trying to acquire the console lock during a panic.
Modify console_trylock() to fail and console_lock() to block() when called from a non-panic CPU during a panic.
Signed-off-by: John Ogness john.ogness@linutronix.de Reviewed-by: Sergey Senozhatsky senozhatsky@chromium.org Reviewed-by: Petr Mladek pmladek@suse.com Signed-off-by: Petr Mladek pmladek@suse.com Link: https://lore.kernel.org/r/20230717194607.145135-4-john.ogness@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/printk/printk.c | 45 ++++++++++++++++++++++++------------------ 1 file changed, 26 insertions(+), 19 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 7d3f30eb35862..591c11888200d 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2585,6 +2585,25 @@ static int console_cpu_notify(unsigned int cpu) return 0; }
+/* + * Return true when this CPU should unlock console_sem without pushing all + * messages to the console. This reduces the chance that the console is + * locked when the panic CPU tries to use it. + */ +static bool abandon_console_lock_in_panic(void) +{ + if (!panic_in_progress()) + return false; + + /* + * We can use raw_smp_processor_id() here because it is impossible for + * the task to be migrated to the panic_cpu, or away from it. If + * panic_cpu has already been set, and we're not currently executing on + * that CPU, then we never will be. + */ + return atomic_read(&panic_cpu) != raw_smp_processor_id(); +} + /** * console_lock - block the console subsystem from printing * @@ -2597,6 +2616,10 @@ void console_lock(void) { might_sleep();
+ /* On panic, the console_lock must be left to the panic cpu. */ + while (abandon_console_lock_in_panic()) + msleep(1000); + down_console_sem(); if (console_suspended) return; @@ -2615,6 +2638,9 @@ EXPORT_SYMBOL(console_lock); */ int console_trylock(void) { + /* On panic, the console_lock must be left to the panic cpu. */ + if (abandon_console_lock_in_panic()) + return 0; if (down_trylock_console_sem()) return 0; if (console_suspended) { @@ -2633,25 +2659,6 @@ int is_console_locked(void) } EXPORT_SYMBOL(is_console_locked);
-/* - * Return true when this CPU should unlock console_sem without pushing all - * messages to the console. This reduces the chance that the console is - * locked when the panic CPU tries to use it. - */ -static bool abandon_console_lock_in_panic(void) -{ - if (!panic_in_progress()) - return false; - - /* - * We can use raw_smp_processor_id() here because it is impossible for - * the task to be migrated to the panic_cpu, or away from it. If - * panic_cpu has already been set, and we're not currently executing on - * that CPU, then we never will be. - */ - return atomic_read(&panic_cpu) != raw_smp_processor_id(); -} - /* * Check if the given console is currently capable and allowed to print * records.