linux-kernel - Re: [PATCH 5.12 123/363] watchdog: cleanup handling of false positives

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Date:   Tue, 18 May 2021 08:55:17 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Laurence Oberman <loberman@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.12 123/363] watchdog: cleanup handling of false
 positives

On (21/05/17 16:30), Petr Mladek wrote:
> On Mon 2021-05-17 15:59:49, Greg Kroah-Hartman wrote:
> > From: Petr Mladek <pmladek@...e.com>
> > 
> > [ Upstream commit 9bf3bc949f8aeefeacea4b1198db833b722a8e27 ]
> > 
> > Commit d6ad3e286d2c ("softlockup: Add sched_clock_tick() to avoid kernel
> > warning on kgdb resume") introduced touch_softlockup_watchdog_sync().
> 
> [...]
> 
> > Make the code more straightforward:
> > 
> > 1. Always call kvm_check_and_clear_guest_paused() at the very
> >    beginning to handle PVCLOCK_GUEST_STOPPED. It touches the watchdog
> >    when the quest did sleep.
> > 
> > 2. Handle the situation when the watchdog has been touched
> >    (SOFTLOCKUP_DELAY_REPORT is set).
> > 
> >    Call sched_clock_tick() when touch_*sync() variant was used. It makes
> >    sure that the timestamp will be up to date even when it has been
> >    touched in atomic context or quest did sleep.
> > 
> > As a result, kvm_check_and_clear_guest_paused() is called on a single
> > location.  And the right timestamp is always set when returning from the
> > timer callback.
> > 
> > Link: https://lkml.kernel.org/r/20210311122130.6788-7-pmladek@suse.com
> 
> Please, remove this patch from the stable backport. It might
> cause false softlockup reports, see

Oh, I didn't know about the stable backport. Thank you for taking care of it.