linux-ext4 - Re: [4.7-rc6 ext3 BUG] kernel BUG at fs/ext4/xattr.c:1331

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Date:	Fri, 29 Jul 2016 08:42:10 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Jan Kara <jack@...e.cz>, Eric Sandeen <sandeen@...hat.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [4.7-rc6 ext3 BUG] kernel BUG at fs/ext4/xattr.c:1331

On Fri 29-07-16 10:21:12, Dave Chinner wrote:
> On Thu, Jul 28, 2016 at 03:54:32PM +0200, Jan Kara wrote:
> > On Mon 18-07-16 15:24:47, Dave Chinner wrote:
> > > On Sun, Jul 17, 2016 at 09:07:16PM -0700, Eric Sandeen wrote:
> > > > On 7/17/16 8:02 PM, Dave Chinner wrote:
> > > > > # rm !$
> > > > > rm /mnt/scratch/fsr_test_file.27768.14.6
> > > > > #
> > > > > 
> > > > > And, by removing an attribute, I can successfully remove the file.
> > > > > So this definitely looks like a corner case xattr handling issue in
> > > > > ext3/4.
> > > > 
> > > > I told xfs/227 that it could run on ext3 and ran it, but this
> > > > didn't reproduce for me.
> > > > 
> > > > Can you provide a dumpe2fs -h for the root fs, this might depend on
> > > > inode size etc.
> > > 
> > > # dumpe2fs -h /dev/sda1
> > > dumpe2fs 1.43-WIP (18-May-2015)
> > > Filesystem volume name:   <none>
> > > Last mounted on:          /
> > > Filesystem UUID:          b21615e5-fe8a-4ffc-ab80-c24cdc8b740a
> > > Filesystem magic number:  0xEF53
> > > Filesystem revision #:    1 (dynamic)
> > > Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file
> > > Filesystem flags:         signed_directory_hash 
> > > Default mount options:    (none)
> > > Filesystem state:         clean
> > > Errors behavior:          Continue
> > > Filesystem OS type:       Linux
> > > Inode count:              624624
> > > Block count:              2496091
> > > Reserved block count:     124804
> > > Free blocks:              567319
> > > Free inodes:              352653
> > > First block:              0
> > > Block size:               4096
> > > Fragment size:            4096
> > > Reserved GDT blocks:      609
> > > Blocks per group:         32768
> > > Fragments per group:      32768
> > > Inodes per group:         8112
> > > Inode blocks per group:   507
> > > Filesystem created:       Thu Mar 25 18:10:55 2010
> > > Last mount time:          Tue Jul 19 01:21:57 2016
> > > Last write time:          Tue Jul 19 01:21:57 2016
> > > Mount count:              10
> > > Maximum mount count:      27
> > > Last checked:             Mon Jul 18 21:59:01 2016
> > > Check interval:           15552000 (6 months)
> > > Next check after:         Sat Jan 14 22:59:01 2017
> > > Lifetime writes:          13 GB
> > > Reserved blocks uid:      0 (user root)
> > > Reserved blocks gid:      0 (group root)
> > > First inode:              11
> > > Inode size:               256
> > > Required extra isize:     28
> > > Desired extra isize:      28
> > > Journal inode:            8
> > > First orphan inode:       219355
> > > Default directory hash:   half_md4
> > > Directory Hash Seed:      740ffa95-af8d-4e89-b68c-5e768a27ece3
> > > Journal backup:           inode blocks
> > > Journal features:         journal_incompat_revoke
> > > Journal size:             128M
> > > Journal length:           32768
> > > Journal sequence:         0x01c975b5
> > > Journal start:            12
> > 
> > Thanks for report! So I see at least part of what happened: Your filesystem
> > was created with 'extra inode size' 28 and likely your inodes were created
> > with this amount of space reserved in the extended attribute area of the
> > inode because you still created them with some older kernel (but that means
> > that it had to be a kernel prior to commit 8b4953e13f4c which landed in
> > 4.4-rc5 because newer kernels would automatically reserve 32-bytes in the
> > inode, not 28 as specified by the superblock).
> 
> Well, yes, the filesystems were made prior to 4.4.-rc5. Only by a
> little - it was made back in January 2010 and has been in use ever
> since. :P
> 
> > The above mentioned commit has added project ID to the inode so new kernels
> > now ask for 32 bytes in the extended attribute area. So when you tried to
> > modify the inode with newer kernel, we were trying to shift extended
> > attributes around to make space for those additional 4 bytes. So that makes
> > it clear why Eric was not able to reproduce the issue.
> 
> Gotcha.
> 
> > I've tried creating file with an old kernel and deleting it with a new one
> > and the bugon indeed triggers. Going through ext4_expand_extra_isize_ea() I
> > see so many bugs that it's not nice. I guess we should add some inode size
> > expansion tests...
> 
> Ouch. At least the problem is understood now - any idea on how long
> it might take to fix?

I have written some fixes, working on testing them... So hopefully I can
submit them later today or next week.

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