linux-kernel - Re: fs: gpf in simple

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Message-ID: <20140325173340.GB17292@quack.suse.cz>
Date:	Tue, 25 Mar 2014 18:33:40 +0100
From:	Jan Kara <jack@...e.cz>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Jan Kara <jack@...e.cz>, Al Viro <viro@...IV.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: fs: gpf in simple_setattr

On Mon 24-03-14 20:44:14, Sasha Levin wrote:
> On 03/24/2014 05:48 PM, Jan Kara wrote:
> >>>[  339.948946] ** 4194304 ffff8805ac03ba38 [eventpoll] ffff8806ec051fe0
> >>>[eventpoll] ffffffff84666040 ffff88056c73e7b0           (null)
> >   OK, great. So finally we have something useful. We know we have problems
> >with [eventpoll] dentry. That is actually a special filesystem not mounted
> >anywhere - likely you get to that dentry through/proc/<pid>/fd/. Now
> >eventpoll is interesting because it uses single anon inode for all
> >eventpoll instances. And that inode should stay in place as long as
> >eventpoll filesystem exists. So it's not clear how come that inode is
> >freed. The basic check of handling of inode use count didn't find anything
> >suspicious. But I can check in more detail and if I fail, we now have a
> >pretty narrow area where to look...
> 
> Seems like it's not specific to eventpoll, I saw the same error message with
> "eventfd" and "perf_event".
  Yup, all these use anon_inode_getfile() so it all points to the fact that
for some reason we freed anon_inode_inode. But I don't see where the
problem is. Can you maybe make 'anon_inode_inode' external to
fs/anon_inodes.c and dump stack for all iput() calls to anon_inode_inode?
There must be some suckers which don't belong there...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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