linux-kernel - Re: [RFT PATCH] blkio: alloc per cpu data from worker thread context( Re: kvm deadlock)

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Message-ID: <20111219134012.GA7175@redhat.com>
Date:	Mon, 19 Dec 2011 08:40:12 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Nate Custer <nate@...nel.net>
Cc:	Jens Axboe <axboe@...nel.dk>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH] blkio: alloc per cpu data from worker thread
 context( Re: kvm deadlock)

On Sun, Dec 18, 2011 at 03:25:48PM -0600, Nate Custer wrote:
> 
> On Dec 16, 2011, at 2:29 PM, Vivek Goyal wrote:
> > Thanks for testing it Nate. I did some debugging and found out that patch
> > is doing double free on per cpu pointer hence the crash you are running
> > into. I could reproduce this problem on my box. It is just a matter of
> > doing rmdir on the blkio cgroup.
> > 
> > I understood the cmpxchg() semantics wrong. I have fixed it now and
> > no crashes on directory removal. Can you please give this version a
> > try.
> > 
> > Thanks
> > Vivek
> 
> After 24 hours of stress testing the machine remains up and working without issue. I will continue to test it, but am reasonably confident that this patch resolves my issue.

That's good to know. While you continue to stress test, I will make some
minor modifications to the patch. (Thinking of delaying the retry of
allocation of per cpu memory in case previous attempts failed).

Thanks
Vivek
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