linux-kernel - Re: EXT4-fs error (device dm-42): ext4_mb_generate_buddy:741: group 1904, 32254 clusters in bitmap, 32258 in gd

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Date:	Tue, 5 Jun 2012 23:35:14 +0200
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Ted Ts'o <tytso@....edu>
CC:	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<dm-devel@...hat.com>, <linux-ext4@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: EXT4-fs error (device dm-42): ext4_mb_generate_buddy:741: group 1904, 32254 clusters in bitmap, 32258 in gd

Hello Ted,

Tuesday, June 5, 2012, 11:08:06 PM, you wrote:

> On Tue, Jun 05, 2012 at 10:41:54PM +0200, Sander Eikelenboom wrote:
>> 
>> > Today I've finally managed to bisect this to here:
>> > [fd034a84e1ea5c8c8d159cd2089c32e792c269b0] ext4: split out ext4_free_blocks_after_init()
>> 
>> > If I revert all the "ext4:" patches in 3.2 up to and including that one,
>> > I get normal behavior again.

> This is excellent.  Thanks!  I'll take a deep look at that ocmmit to
> see what might be going on.

>> So somehow this only effects ext4 on DM (it's THE common factor in all reports) and fsck seems incapable of seeing the error (and thus repair it.)

> What's probably happening is it's only the in-memory copy of the
> bitmap which is getting corrupted, and because the file system is
> getting remounted read-only, the corrupted bitmap is not getting
> written back to disk.  (This is the whole point of remount-ro when fs
> corruptions are detected.  :-)

The commits Kees pointed too, made me:

- Copy files to the fs and trigger the error.
- "fsck -v -f", no errors where reported, only journal recovered.
- "tune2fs -O ^uninit_bg" on the fs.
- "fsck -v -f", which found some bitmap size errors now, let it fix these.
- Mounted the fs
- Copy the same set of files, no error has occured.

So it seems related to the uninit_bg changes in the commits on 10 september 2011.

--
Sander



> Cheers,

>                                                 - Ted




-- 
Best regards,
 Sander                            mailto:linux@...elenboom.it

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