linux-kernel - Re: fs: locks: WARNING: CPU: 16 PID: 4296 at fs/locks.c:236 locks_free_lock

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Message-ID: <20150116135304.0feeaf15@tlielax.poochiereds.net>
Date:	Fri, 16 Jan 2015 13:53:04 -0500
From:	Jeff Layton <jeff.layton@...marydata.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Jeff Layton <jeff.layton@...marydata.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: fs: locks: WARNING: CPU: 16 PID: 4296 at fs/locks.c:236
 locks_free_lock_context+0x10d/0x240()

On Fri, 16 Jan 2015 13:10:46 -0500
Sasha Levin <sasha.levin@...cle.com> wrote:

> On 01/16/2015 09:40 AM, Jeff Layton wrote:
> > On Fri, 16 Jan 2015 09:31:23 -0500
> > Sasha Levin <sasha.levin@...cle.com> wrote:
> > 
> >> On 01/15/2015 03:22 PM, Jeff Layton wrote:
> >>> Ok, I tried to reproduce it with that and several variations but it
> >>> still doesn't seem to do it for me. Can you try the latest linux-next
> >>> tree and see if it's still reproducible there?
> >>
> >> It's still not in in today's -next, could you send me a patch for testing
> >> instead?
> >>
> > 
> > Seems to be there for me:
> > 
> > ----------------------[snip]-----------------------
> > /*
> >  * This function is called on the last close of an open file.
> >  */
> > void locks_remove_file(struct file *filp)
> > {
> >         /* ensure that we see any assignment of i_flctx */
> >         smp_rmb();
> > 
> >         /* remove any OFD locks */
> >         locks_remove_posix(filp, filp);
> > ----------------------[snip]-----------------------
> > 
> > That's actually the right place to put the barrier, I think. We just
> > need to ensure that this function sees any assignment to i_flctx that
> > occurred before this point. By the time we're here, we shouldn't be
> > getting any new locks that matter to this close since the fcheck call
> > should fail on any new requests.
> > 
> > If that works, then I'll probably make some other changes to the set
> > and re-post it next week.
> > 
> > Many thanks for helping me test this!
> 
> You're right, I somehow missed that.
> 
> But it doesn't fix the issue, I still see it happening, but it seems
> to be less frequent(?).
> 

Ok, that was my worry (and one of the reasons I really would like to
find some way to reproduce this on my own). I think what I'll do at
this point is pull the patchset from linux-next until I can consult
with someone who understands this sort of cache-coherency problem
better than I do.

Once I get it resolved, I'll push it back to my linux-next branch and
let you know and we can give it another go.

Thanks for the testing so far!
-- 
Jeff Layton <jlayton@...marydata.com>
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