linux-ext4 - Re: [PATCH] ext3: fix message in ext3

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Message-ID: <4E38B57B.4050304@jp.fujitsu.com>
Date:	Wed, 03 Aug 2011 11:42:03 +0900
From:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
To:	Jan Kara <jack@...e.cz>
CC:	akpm@...ux-foundation.org, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext3: fix message in ext3_remount for rw-remount case

Hi.

(2011/08/02 18:14), Toshiyuki Okajima wrote:
> Hi.
>
> (2011/08/01 18:57), Jan Kara wrote:
>> On Mon 01-08-11 18:45:58, Toshiyuki Okajima wrote:
>>> (2011/08/01 17:45), Jan Kara wrote:
>>>> On Mon 01-08-11 13:54:51, Toshiyuki Okajima wrote:
>>>>> If there are some inodes in orphan list while a filesystem is being
>>>>> read-only mounted, we should recommend that pepole umount and then
>>>>> mount it when they try to remount with read-write. But the current
>>>>> message/comment recommends that they umount and then remount it.
<SNIP>
>>>> the most... BTW, I guess you didn't really see this message in practice, did
>>>> you?
>>> No.
>>> I have seen this message in practice while quotacheck command was repeatedly
>>> executed per an hour.
>> Interesting. Are you able to reproduce this? Quotacheck does remount
>> read-only + remount read-write but you cannot really remount the filesystem
>> read-only when it has orphan inodes and so you should not see those when
>> you remount read-write again. Possibly there's race between remounting and
>> unlinking...
> Yes. I can reproduce it. However, it is not frequently reproduced
> by using the original procedure (qutacheck per an hour). So, I made a
> reproducer.
To tell the truth, I think the race creates the message:
-----------------------------------------------------------------------
  EXT3-fs: <dev>: couldn't remount RDWR because of
  　　　 　unprocessed orphan inode list.  Please umount/remount instead.
-----------------------------------------------------------------------
which hides a serious problem.

By using my reproducer, I found that it can show another message that
is not the above mentioned message:
-----------------------------------------------------------------------
EXT3-fs error (device <dev>) in start_transaction: Readonly filesystem	
-----------------------------------------------------------------------
After I examined the code path which message could display, I found
it can display if the following steps are satisfied:

[[CASE 1]]
( 1)  [process A] do_unlinkat
( 2)  [process B] do_remount_sb(, RDONLY, )
( 3)  [process A]  vfs_unlink
( 4)  [process A]   ext3_unlink
( 5)  [process A]    ext3_journal_start
( 6)  [process B]  fs_may_remount_ro   (=> return 0)
( 7)  [process A]    inode->i_nlink-- (i_nlink=0)
( 8)  [process A]    ext3_orphan_add
( 9)  [process A]    ext3_journal_stop
(10)  [process A]  dput
(11)  [process A]   iput
(12)  [process A]    ext3_evict_inode
(13)  [process B]  ext3_remount
(14)  [process A]     start_transaction
(15)  [process B]   sb->s_flags |= MS_RDONLY
(16)  [process B]   ext3_mark_recovery_complete
(17)  [process A]      start_this_handle (new transaction is created)
(18)  [process A]     ext3_truncate
(19)  [process A]      start_transaction (failed => this message is displayed)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(20)  [process A]     ext3_orphan_del
(21)  [process A]     ext3_journal_stop

* "Process A" deletes a file successfully(21). However the file data is left
    because (18) fails. **Furthermore, new transaction can be created after
    ext3_mark_recovery_complete finishes.**

[[CASE2]]
( 1)  [process A] do_unlinkat
( 2)  [process B] do_remount_sb(, RDONLY, )
( 3)  [process A]  vfs_unlink
( 4)  [process A]   ext3_unlink
( 5)  [process A]    ext3_journal_start
( 6)  [process B]  fs_may_remount_ro   (=> return 0)
( 7)  [process A]    inode->i_nlink-- (i_nlink=0)
( 8)  [process A]    ext3_orphan_add
( 9)  [process A]    ext3_journal_stop
(10)  [process A]  dput
(11)  [process A]   iput
(12)  [process A]    ext3_evict_inode
(13)  [process B]  ext3_remount
(14)  [process A]     start_transaction
(15)  [process B]   sb->s_flags |= MS_RDONLY
(17)  [process A]      start_this_handle (new transaction is created)
(18)  [process A]     ext3_truncate
(19)  [process A]      start_transaction (failed => this message is displayed)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(20)  [process A]     ext3_orphan_del
(21)  [process A]     ext3_journal_stop
(22)  [process B]   ext3_mark_recovery_complete

* "Process A" deletes a file successfully(21). However the file data is left
    because (18) fails. This transaction can finish before
    ext3_mark_recovery_complete finishes.

I will try to fix this problem not to do with fs-error.
Please comment about the fix if I have created one.

Thanks,
Toshiyuki Okajima

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