linux-kernel - Re: fs: gpf in simple

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Message-ID: <20140325211229.GA27422@quack.suse.cz>
Date:	Tue, 25 Mar 2014 22:12:29 +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 Tue 25-03-14 13:51:11, Sasha Levin wrote:
> On 03/25/2014 01:33 PM, Jan Kara wrote:
> >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...
> 
> Okay, this is straightforward. It happened right after boot so we're lucky.
> 
> I'm also looking into that, but odds you'll spot the issue faster than me.
  Can you try whether the following patch fixes the issue for you?

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

View attachment "0001-fs-Avoid-userspace-mounting-anon_inodefs-filesystem.patch" of type "text/x-patch" (1304 bytes)