linux-kernel - Re: [PATCH] epoll: clear the tfile_check

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Message-ID: <20120419153428.GA1596@redhat.com>
Date:	Thu, 19 Apr 2012 11:34:35 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	"Alexandra N. Kossovsky" <Alexandra.Kossovsky@...etlabs.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Yurij.Plotnikov@...etlabs.ru, davidel@...ilserver.org,
	nelhage@...hage.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] epoll: clear the tfile_check_list on -ELOOP

On Wed, Apr 18, 2012 at 08:56:15AM +0400, Alexandra N. Kossovsky wrote:
> On Tue, Apr 17, 2012 at 02:13:15PM -0700, Andrew Morton wrote:
> > On Tue, 17 Apr 2012 10:34:52 -0400
> > Jason Baron <jbaron@...hat.com> wrote:
> > 
> > > An epoll_ctl(,EPOLL_CTL_ADD,,) operation can return '-ELOOP' to prevent
> > > circular epoll dependencies from being created. However, in that case
> > > we do not properly clear the 'tfile_check_list'. Thus, add a call to
> > > clear_tfile_check_list() for the -ELOOP case.
> > 
> > So here I am wondering what effect this bug has upon our users, so I
> > can decide which kernel versions should be fixed.  Jason didn't tell me
> > so I went to read the description of clear_tfile_check_list().  After a
> > brief chuckle, I stopped.
> > 
> > I then found Yurij's original report, so I know what's going on.  But I
> > still can't write your changelog because I don't know whether this is a
> > regression and if it is, which patch caused the regression.
> 
> It is a regression, somewhere between 3.2.6 and 3.2.9.
> Yurij and me blame
> commit 203aa5260edca2ab1872ad8b08386d874f7132f3
> Author: Jason Baron <jbaron@...hat.com>
> Date:   Thu Jan 12 17:17:43 2012 -0800
> but we have not tested it.
> 

Right, I introduced this with the upstream commit:

commit 28d82dc1c4edbc352129f97f4ca22624d1fe61de
Author: Jason Baron <jbaron@...hat.com>
Date:   Thu Jan 12 17:17:43 2012 -0800

    epoll: limit paths

So yes, this is a newly introduced regression.

Thanks,

-Jason
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