linux-kernel - Re: kernel BUG at fs/btrfs/extent-tree.c:1353

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Date:	Thu, 29 Jul 2010 20:54:58 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Johannes Hirte <johannes.hirte@....tu-ilmenau.de>
CC:	miaox@...fujitsu.com, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	zheng.yan@...cle.com, linux-fsdevel@...r.kernel.org
Subject: Re: kernel BUG at fs/btrfs/extent-tree.c:1353

On 07/29/2010 07:09 PM, Johannes Hirte wrote:
> Am Donnerstag 22 Juli 2010, 20:07:23 schrieb Johannes Hirte:
>> Am Montag 19 Juli 2010, 10:01:46 schrieb Miao Xie:
>>> On Thu, 15 Jul 2010 20:14:51 +0200, Johannes Hirte wrote:
>>>> Am Donnerstag 15 Juli 2010, 02:11:04 schrieb Dave Chinner:
>>>>> On Wed, Jul 14, 2010 at 05:25:23PM +0200, Johannes Hirte wrote:
>>>>>> Am Donnerstag 08 Juli 2010, 16:31:09 schrieb Chris Mason:
>>>>>> I'm not sure if btrfs is to blame for this error. After the errors I
>>>>>> switched to XFS on this system and got now this error:
>>>>>>
>>>>>> ls -l .kde4/share/apps/akregator/data/
>>>>>> ls: cannot access .kde4/share/apps/akregator/data/feeds.opml:
>>>>>> Structure needs cleaning
>>>>>> total 4
>>>>>> ?????????? ? ?    ?        ?            ? feeds.opml
>>>>>
>>>>> What is the error reported in dmesg when the XFS filesytem shuts down?
>>>>
>>>> Nothing. I double checked the logs. There are only the messages when
>>>> mounting the filesystem. No other errors are reported than the
>>>> inaccessible file and the output from xfs_check.
>>>
>>> Is there anything wrong with your disks or memory?
>>> Sometimes the bad memory can break the filesystem. I have met this kind
>>> of problem some time ago.
>>
>> I don't think that's the case. I've checked the RAM with memtest86+ and got
>> no errors. I got the errors with two different disks, the first one with
>> btrfs the second one now with XFS. Before changing to the second disk,
>> I've run badblocks on it to be sure it has no errors.
> 
> I think I've found it. The bug was introduced by 
> 
> commit 7f0e7bed936a0c422641a046551829a01341dd80
> Author: Christoph Hellwig <hch@....de>
> Date:   Tue Jun 8 18:14:34 2010 +0200
> 
>     writeback: fix writeback completion notifications
>     
>     The code dealing with bdi_work->state and completion of a bdi_work is a
>     major mess currently.  This patch makes sure we directly use one set of
>     flags to deal with it, and use it consistently, which means:
>     
>      - always notify about completion from the rcu callback.  We only ever
>        wait for it from on-stack callers, so this simplification does not
>        even cause a theoretical slowdown currently.  It also makes sure we
>        don't miss out on the notification if we ever add other callers to
>        wait for it.
>      - make earlier completion notification depending on the on-stack
>        allocation, not the sync mode.  If we introduce new callers that
>        want to do WB_SYNC_NONE writeback from on-stack callers this will
>        be nessecary.
>     
>     Also rename bdi_wait_on_work_clear to bdi_wait_on_work_done and inline
>     a few small functions into their only caller to make the code
>     understandable.
>     
>     Signed-off-by: Christoph Hellwig <hch@....de>
>     Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
> 
> and seems to be fixed by
> 
> commit 83ba7b071f30f7c01f72518ad72d5cd203c27502
> Author: Christoph Hellwig <hch@....de>
> Date:   Tue Jul 6 08:59:53 2010 +0200
> 
>     writeback: simplify the write back thread queue
>     
>     First remove items from work_list as soon as we start working on them.This
>     means we don't have to track any pending or visited state and can get
>     rid of all the RCU magic freeing the work items - we can simply free
>     them once the operation has finished.  Second use a real completion for
>     tracking synchronous requests - if the caller sets the completion pointer
>     we complete it, otherwise use it as a boolean indicator that we can free
>     the work item directly.  Third unify struct wb_writeback_args and struct
>     bdi_work into a single data structure, wb_writeback_work.  Previous we
>     set all parameters into a struct wb_writeback_args, copied it into
>     struct bdi_work, copied it again on the stack to use it there.  Instead
>     of just allocate one structure dynamically or on the stack and use it
>     all the way through the stack.
>     
>     Signed-off-by: Christoph Hellwig <hch@....de>
>     Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
> 
> I was able to reproduce the bug by unpacking a big tar-file and
> deleting this files multiple times. Normally with btrfs the kernel
> crashed within 20 runs. After commit
> 83ba7b071f30f7c01f72518ad72d5cd203c27502 it survived more than 500
> runs.

Makes sense, that first commit would potentially pass in stack cruft as
the wbc arg. So I think we can safely consider it fixed now.

-- 
Jens Axboe

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