linux-kernel - RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups

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Date:   Mon, 17 Jul 2017 12:18:45 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Don Zickus <dzickus@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "babu.moger@...cle.com" <babu.moger@...cle.com>,
        "atomlin@...hat.com" <atomlin@...hat.com>,
        "prarit@...hat.com" <prarit@...hat.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "acme@...hat.com" <acme@...hat.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH V2] kernel/watchdog: fix spurious hard lockups

> 
> On Mon, 17 Jul 2017, Liang, Kan wrote:
> > There are three proposed patches so far.
> > Patch 1: The patch as above which speed up the hrtimer.
> > Patch 2: Thomas's first proposal.
> > https://patchwork.kernel.org/patch/9803033/
> > https://patchwork.kernel.org/patch/9805903/
> > Patch 3: my original proposal which increase the NMI watchdog timeout
> > by 3X https://patchwork.kernel.org/patch/9802053/
> >
> > According to our test, only patch 3 works well.
> > The other two patches will hang the system eventually.
> > For patch 1, the system hang after running our test case for ~1 hour.
> > For patch 2, the system hang in running the overnight test.
> > There is no error message shown when the system hang. So I don't know
> > the root cause yet.
> 
> That doesn't make sense. What's the exact test procedure?

I don't know the exact test procedure. The test case is from our customer.
I only know that the test case makes calls into the x11 libs.

> 
> > BTW: We set 1 to watchdog_thresh when we did the test.
> > It's believed that can speed up the failure.
> 
> Believe is not really a technical measure....
> 

1 is a valid value for watchdog_thresh.
It was set through the standard proc interface.
/proc/sys/kernel/watchdog_thresh
It should not impacts the final test result.

Thanks,
Kan