From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Stephen Brennan <stephen.s.brennan@oracle.com>,
Petr Mladek <pmladek@suse.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: Wed, 26 Jan 2022 19:06:44 +0900 [thread overview]
Message-ID: <YfEdNKWI7GqKr9P/@google.com> (raw)
In-Reply-To: <87r18un83x.fsf@jogness.linutronix.de>
On (22/01/26 10:51), John Ogness wrote:
> > Is there something that prevents panic CPU from NMI hlt CPU which is
> > in console_trylock() under raw_spin_lock_irqsave()?
> >
> > CPU0 CPU1
> > console_trylock_spinnning()
> > console_trylock()
> > down_trylock()
> > raw_spin_lock_irqsave(&sem->lock)
> >
> > panic()
> > crash_smp_send_stop()
> > NMI -> HALT
>
> This is a good point. I wonder if console_flush_on_panic() should
> perform a sema_init() before it does console_trylock().
A long time ago there was zap_locks() function in printk, that used
to re-init console semaphore and logbuf spin_lock, but _only_ in case
of printk recursion (which was never reliable)
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/kernel/printk/printk.c?h=v4.9.297#n1557
This has been superseded by printk_safe per-CPU buffers so we removed
that function.
So it could be that may be we want to introduce something similar to
zap_locks() again.
All reasonable serial consoles drivers should take oops_in_progress into
consideration in ->write(), so we probably don't care for console_drivers
spinlocks, etc. but potentially can do a bit better on the printk side.
next prev parent reply other threads:[~2022-01-26 10:06 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 [this message]
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
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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