Date: Tue, 15 Mar 2016 10:28:58 -0400
From: Don Zickus <dzickus@redhat.com>
To: Josh Hunt <johunt@akamai.com>
Cc: akpm@linux-foundation.org, uobergfe@redhat.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] watchdog: don't run proc_watchdog_update if new value is
 same as old
Message-ID: <20160315142858.GZ194535@redhat.com>
References: <1457826627-21727-1-git-send-email-johunt@akamai.com>
 <20160314143426.GK194535@redhat.com>
 <56E6CE86.5070606@akamai.com>
 <20160314162955.GQ194535@redhat.com>
 <56E78957.6020707@akamai.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <56E78957.6020707@akamai.com>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1935
Lines: 55

On Mon, Mar 14, 2016 at 11:02:31PM -0500, Josh Hunt wrote:
> On 03/14/2016 11:29 AM, Don Zickus wrote:
> >
> >Hi Josh,
> >
> >I believe Uli thought the below patch might fix it.
> >
> >Cheers,
> >Don
> 
> Don
> 
> It looks like I was incorrect when I said 4.5 was getting the soft lockup. I
> originally found this problem on 4.1.19 and saw both the problem my patch
> solves and the soft lockups there. I thought when I checked 4.5 that I saw
> both issues there as well, but going back and checking now that is not the
> case. I only see the issue my patch resolves on 4.5.
> 
> With that info my changelog is incorrect now as it states I saw a soft
> lockup on the head. I will submit a v2 of my patch with the updated
> changelog. I'll also cc stable this time as I'd like to see this fix end up
> there as well.
> 
> As for the soft lockups showing up on 4.1, I tried Uli's patch and it did
> not help. After that I did a git bisect to figure out when the soft lockup
> was fixed and it appears to be resolved after one of the commits in this
> series:
> 
> commit 81a4beef91ba4a9e8ad6054ca9933dff7e25ff28
> Author: Ulrich Obergfell <uobergfe@redhat.com>
> Date:   Fri Sep 4 15:45:15 2015 -0700
> 
>     watchdog: introduce watchdog_park_threads() and
> watchdog_unpark_threads()
> 
> I didn't identify the exact commit.
> 
> It would be nice to resolve the soft lockup for the stable folks since 4.1
> and 4.4 are longterm stable releases and would see this problem.
> 
> I did not have time to debug it any more outside of this bisection today. If
> you have something you'd like me to try which may work for the stable
> kernels I'm happy to test it.
> 
> For the record I'm able to reproduce the soft lockup on 4.1 doing:
> 
> while :; do echo 1 > /proc/sys/kernel/nmi_watchdog; sleep .1; done & sleep
> 30 && kill %1 && sleep 5


Thanks for the feedback Josh!  Good to know the softlockup was fixed
already. :-)

Cheers,
Don