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

From: Jens Axboe
Date: Thu Jul 29 2010 - 14:55:26 EST

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@xxxxxx>
> 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@xxxxxx>
> Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
> and seems to be fixed by
> commit 83ba7b071f30f7c01f72518ad72d5cd203c27502
> Author: Christoph Hellwig <hch@xxxxxx>
> 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@xxxxxx>
> Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
> 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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