Date: Thu, 10 Dec 2015 10:29:01 -0500
From: Tejun Heo <tj@kernel.org>
To: Nikolay Borisov <kernel@kyup.com>
Cc: "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        SiteGround Operations <operations@siteground.com>
Subject: Re: corruption causing crash in __queue_work
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On Thu, Dec 10, 2015 at 11:28:02AM +0200, Nikolay Borisov wrote:
> On 12/09/2015 06:27 PM, Tejun Heo wrote:
> > Hello,
> > 
> > On Wed, Dec 09, 2015 at 06:23:15PM +0200, Nikolay Borisov wrote:
> >> I think we are seeing this at least daily on at least 1 server (we have
> >> multiple servers like that). So adding printk's would likely be the way
> >> to go, anything in particular you might be interested in knowing? I see
> >> RCU stuff around so might be tricky race condition.
> > 
> > Printing out the workqueue's pointer, name, pwq's pointer, the node
> > being installed for and the installed pointer should give us enough
> > clues.  There's RCU involved but the pointers shouldn't be becoming
> > NULLs unless we're installing NULL ptrs.
> 
> So the debug patch has been rolled on 1 server and several more 
> are in the process, here it is what it prints: 
> 
> WQ: ffff88046f00ba00 (events_unbound) old_pwq:           (null) new_pwq: ffff88046f00d300 node: 0
...
> Is this format ok? Also I observed the exact same crash
> on a machine running 4.1.12 kernel as well. 

Yeah, I think it can be a good starting point.

Thanks.

-- 
tejun
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