From: Stephen Brennan <stephen.s.brennan@xxxxxxxxxx> [ Upstream commit 8ebc476fd51e6c0fd3174ec1959a20ba99d4c5e5 ] If another CPU is in panic, we are about to be halted. Try to gracefully abandon the console_sem, leaving it free for the panic CPU to grab. Suggested-by: Petr Mladek <pmladek@xxxxxxxx> Signed-off-by: Stephen Brennan <stephen.s.brennan@xxxxxxxxxx> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> Signed-off-by: Petr Mladek <pmladek@xxxxxxxx> Link: https://lore.kernel.org/r/20220202171821.179394-5-stephen.s.brennan@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/printk/printk.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 4f31290256ad..bc5cbdeb38f3 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2588,6 +2588,25 @@ static int have_callable_console(void) 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(); +} + /* * Can we actually use the console at this time on this cpu? * @@ -2736,6 +2755,10 @@ void console_unlock(void) if (handover) return; + /* Allow panic_cpu to take over the consoles safely */ + if (abandon_console_lock_in_panic()) + break; + if (do_cond_resched) cond_resched(); } @@ -2753,7 +2776,7 @@ void console_unlock(void) * flush, no worries. */ retry = prb_read_valid(prb, next_seq, NULL); - if (retry && console_trylock()) + if (retry && !abandon_console_lock_in_panic() && console_trylock()) goto again; } EXPORT_SYMBOL(console_unlock); -- 2.34.1
