From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Arnd Bergmann <arnd@arndb.de>,
Steven Rostedt <rostedt@goodmis.org>,
Andrew Morton <akpm@linux-foundation.org>,
Sebastian Reichel <sre@kernel.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Luis Chamberlain <mcgrof@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/4] printk: Drop console_sem during panic
Date: Thu, 27 Jan 2022 16:03:46 +0100 [thread overview]
Message-ID: <YfK0Ugt/i8nMVOmY@alley> (raw)
In-Reply-To: <87fsp9pm6q.fsf@jogness.linutronix.de>
On Thu 2022-01-27 10:28:53, John Ogness wrote:
> On 2022-01-26, Stephen Brennan <stephen.s.brennan@oracle.com> wrote:
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -2759,7 +2782,7 @@ 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())
>
> As Sergey suggested [0], I would like to see the call to
> abandon_console_lock_in_panic() move inside console_trylock(). This will
> help to avoid the race between NMI CPU halt and the internal sema.lock
> spinlock.
I would prefer if it is done as a followup patch. The code in this
patch is still needed. It helps when the non-panic CPU is busy
with pushing many pending messages. Also it is a more conservative
approach.
Always failing console_trylock() on non-panic CPU makes sense as well.
But it affects many more users. It is likely safe because it is
trylock. But the entire effect is not fully clear to me. So, I suggest
to do it in a separate patch. It might help with bisection.
Best Regards,
Petr
next prev parent reply other threads:[~2022-01-27 15:03 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 23:02 [PATCH v2 0/4] printk: reduce deadlocks during panic Stephen Brennan
2022-01-26 23:02 ` [PATCH v2 1/4] panic: Add panic_in_progress helper Stephen Brennan
2022-01-27 0:29 ` kernel test robot
2022-01-27 0:40 ` kernel test robot
2022-01-27 14:34 ` Petr Mladek
2022-01-27 16:02 ` Stephen Brennan
2022-01-28 8:24 ` Petr Mladek
2022-01-26 23:02 ` [PATCH v2 2/4] printk: disable optimistic spin during panic Stephen Brennan
2022-01-26 23:02 ` [PATCH v2 3/4] printk: Avoid livelock with heavy printk " Stephen Brennan
2022-01-27 14:50 ` Petr Mladek
2022-01-27 16:19 ` Stephen Brennan
2022-01-26 23:02 ` [PATCH v2 4/4] printk: Drop console_sem " Stephen Brennan
2022-01-27 9:22 ` John Ogness
2022-01-27 15:03 ` Petr Mladek [this message]
2022-01-28 5:55 ` Sergey Senozhatsky
2022-01-27 15:12 ` Petr Mladek
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