linux-kernel - Re: [PATCH] watchdog/hardlockup: set watchdog_hardlockup

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Date:   Mon, 7 Aug 2023 15:54:04 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Liu Song <liusong@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, dianders@...omium.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog/hardlockup: set watchdog_hardlockup_warned to
 true as early as possible

On Sun 2023-08-06 10:52:57, Liu Song wrote:
> 
> 在 2023/8/6 01:17, Andrew Morton 写道:
> > When resending, please tell us some more about the effects of the
> > change.  Presumably there are circumstances in which excess output is
> > produced?  If so, describe these circumstances and the observed
> > effects.
> 
> Hi,
> 
> I haven't found duplicate warnings in the real environment.
> 
> However, considering that when system occurs hard lockup is basically
> abnormal, it
> 
> seems more reasonable to set "watchdog_hardlockup_warned" to ture, rather
> than
> 
> waiting for all kinds of information to be printed.

I believe that this is not needed.

watchdog_hardlockup_check(cpu, regs) is called on a CPU periodically.
There are two callers:

   + buddy detector checks the particular CPU when the solflockup's
     hrtimer callback is called. See watchdog_hardlockup_kick()
     in watchdog_timer_fn().

   + perf detector checks the particular CPU from a perf callback,
     see watchdog_overflow_callback().

Neither timer nor perf callbacks might be nested. They are naturally
serialized on a given CPU. So, races are not possible in this case.

Best Regards,
Petr