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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: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-5-stephen.s.brennan@oracle.com
This commit is contained in:
Stephen Brennan 2022-02-02 09:18:21 -08:00 committed by Petr Mladek
parent 13fb0f74d7
commit 8ebc476fd5
1 changed files with 24 additions and 1 deletions
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25
kernel/printk/printk.c
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@ -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 @@ skip:
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 @@ skip:
* 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);