Commit 8ebc476f authored by Stephen Brennan's avatar Stephen Brennan Committed by Petr Mladek
Browse files

printk: Drop console_sem during panic 



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: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarStephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-5-stephen.s.brennan@oracle.com
parent 13fb0f74

kernel/printk/printk.c

+24 −1
Original line number Diff line number Diff line
@@ -2597,6 +2597,25 @@ 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?

 *
@@ -2745,6 +2764,10 @@ 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();

	}
@@ -2762,7 +2785,7 @@ 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);