linux-kernel - Re: [PATCH 2/3] watchdog/softlockup: Report the same softlockup regularly

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Message-ID: <20191021134038.fz2cdpxrd3p3yhb7@pathway.suse.cz>
Date:   Mon, 21 Oct 2019 15:40:38 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Laurence Oberman <loberman@...hat.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] watchdog/softlockup: Report the same softlockup
 regularly

On Mon 2019-10-21 14:43:39, Peter Zijlstra wrote:
> On Mon, Aug 19, 2019 at 12:47:31PM +0200, Petr Mladek wrote:
> > Softlockup report means that there is no progress on the given CPU. It
> > might be a "short" affair where the system gets recovered. But often
> > the system stops being responsive and need to get rebooted.
> > 
> > The softlockup might be root of the problems or just a symptom. It might
> > be a deadlock, livelock, or often repeated state.
> > 
> > Regular reports help to distinguish different situations. Fortunately,
> > the watchdog is finally able to show correct information how long
> > softlockup_fn() was not scheduled.
> > 
> > Report before this patch:
> > 
> > [  320.248948] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4916]
> > 
> > And after this patch:
> > 
> > [  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]
> > 
> > Note that the horrible code never really worked before the accounting
> > was fixed. The last working timestamp was regularly lost by the many
> > touch*watchdog() calls.
> 
> So what's the point of patch 1? Just confusing people?

I was not sure what was the expected behavior. The code actually
looked like only the first report was wanted. But it probably never
worked that way.

Should I squash the two patches and send it again, please?

Best Regards,
Petr