linux-kernel - Re: fs: gpf in simple

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Date:	Tue, 25 Mar 2014 20:12:48 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Jan Kara <jack@...e.cz>
CC:	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 03/25/2014 05:12 PM, Jan Kara wrote:
> 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?

Looks like it fixes it, thanks!


Thanks,
Sasha

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