linux-kernel - Re: [PATCH 0/3] watchdog/softlockup: Make softlockup reports more reliable and useful

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Date:   Mon, 21 Oct 2019 14:32:43 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Laurence Oberman <loberman@...hat.com>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] watchdog/softlockup: Make softlockup reports more
 reliable and useful

On Mon 2019-08-19 12:47:29, Petr Mladek wrote:
> ( Resending this as a proper patch with updated commit messages.
>   The original was
>   https://lkml.kernel.org/r/20190605140954.28471-1-pmladek@suse.com )
> 
> We were analyzing logs with several softlockup reports in flush_tlb_kernel_range().
> They were confusing. Especially it was not clear whether it was deadlock,
> livelock, or separate softlockups.
> 
> It went out that even a simple busy loop:
> 
> 	while (true)
> 	      cpu_relax();
> 
> is able to produce several softlockups reports:
> 
>   [  168.277520] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865]
>   [  196.277604] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865]
>   [  236.277522] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [cat:4865]
>                                                               ^^^^
> 
> This patchset fixes the problem in two steps:
> 
> + 1st patch prevents restart of the watchdog from unrelated locations.
>   Each softlockup is reported only once:
> 
>   [  320.248948] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4916]
> 
> 
> + 2nd patch helps to distinguish several possible situations by
>   regular reports. The report looks like:
> 
>   [  480.372418] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4943]
>   [  508.372359] watchdog: BUG: soft lockup - CPU#2 stuck for 52s! [cat:4943]
>   [  548.372359] watchdog: BUG: soft lockup - CPU#2 stuck for 89s! [cat:4943]
>   [  576.372351] watchdog: BUG: soft lockup - CPU#2 stuck for 115s! [cat:4943]

Gently ping. Is anyone against merging the two fixes, please?

Best Regards,
Petr