From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] printk: disable optimistic spin during panic
Date: Thu, 27 Jan 2022 13:49:44 +0106 [thread overview]
Message-ID: <877dalpcvz.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <YfKEGg0zQqXBVqGG@alley>
On 2022-01-27, Petr Mladek <pmladek@suse.com> wrote:
> I mean that chance of dealock caused by the internal semaohore spin
> lock is super small. In compare, a lot of tricky code is guarded
> by console_sem. It looks like a big risk to ignore the semaphore
> early in panic().
Agreed.
> A better solution would be to use raw_spin_trylock_irqsave() in
> down_trylock().
down_trylock() is attempting to decrement a semaphore. It should not
fail just because another CPU is also in the process of
decrementing/incrementing the semaphore.
Maybe a down_trylock_cond() could be introduced where the trylock could
fail if a given condition is not met. The function would need to
implement its own internal trylock spin loop to check the condition. But
then we could pass in a condition for it to abort. For example, when in
panic and we are not the panic CPU.
John
next prev parent reply other threads:[~2022-01-27 12:43 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-21 19:02 [PATCH 0/4] printk: reduce deadlocks during panic Stephen Brennan
2022-01-21 19:02 ` [PATCH 1/4] panic: Add panic_in_progress helper Stephen Brennan
2022-01-25 11:48 ` Petr Mladek
2022-01-26 17:37 ` Stephen Brennan
2022-01-21 19:02 ` [PATCH 2/4] printk: disable optimistic spin during panic Stephen Brennan
2022-01-25 12:42 ` Petr Mladek
2022-01-26 9:18 ` Sergey Senozhatsky
2022-01-26 9:45 ` John Ogness
2022-01-26 10:06 ` Sergey Senozhatsky
2022-01-26 18:15 ` Stephen Brennan
2022-01-27 7:11 ` Sergey Senozhatsky
2022-01-27 9:09 ` John Ogness
2022-01-27 11:38 ` Petr Mladek
2022-01-27 12:43 ` John Ogness [this message]
2022-01-27 14:25 ` Petr Mladek
2022-01-21 19:02 ` [PATCH 3/4] printk: Avoid livelock with heavy printk " Stephen Brennan
2022-01-25 14:25 ` Petr Mladek
2022-01-21 19:02 ` [PATCH 4/4] printk: Drop console_sem " Stephen Brennan
2022-01-24 16:12 ` John Ogness
2022-01-24 16:26 ` John Ogness
2022-01-25 15:04 ` Petr Mladek
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