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

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Message-ID: <YKJ+INpik2i9IhZN@alley>
Date:   Mon, 17 May 2021 16:30:56 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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 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
https://lore.kernel.org/r/20210517140612.222750-1-senozhatsky@chromium.org

Best Regards,
Petr