linux-ext4 - Re: [PATCH] ext4: fix data=journal fast mount/umount hang

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Date:	Wed, 20 Mar 2013 14:38:11 +0100
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>, stable@...r.kernel.org
Subject: Re: [PATCH] ext4: fix data=journal fast mount/umount hang

On Wed 20-03-13 08:37:37, Ted Tso wrote:
> In data=journal mode, if we unmount the file system before a
> transaction has a chance to complete, when the journal inode is being
> evicted, we can end up calling into jbd2_log_wait_commit() for the
> current transaction.
> 
> Arguably we should adjust ext4_should_journal_data() to return FALSE
> for the journal inode, but the only place it matters is
> ext4_evict_inode(), and so it's to save a bit of CPU time, and to make
> the patch much more obviously correct by inspection(tm), we'll fix it
> by explicitly not trying to waiting for a journal commit when we are
> evicting the journal inode, since it's guaranteed to never succeed in
> this case.
> 
> This can be easily replicated via:
> 
>      mount -t ext4 -o data=journal /dev/vdb /vdb ; umount /vdb
> 
> ------------[ cut here ]------------
> WARNING: at /usr/projects/linux/ext4/fs/jbd2/journal.c:542 __jbd2_log_start_commit+0xba/0xcd()
> Hardware name: Bochs
> JBD2: bad log_start_commit: 3005630206 3005630206 0 0
> Modules linked in:
> Pid: 2909, comm: umount Not tainted 3.8.0-rc3 #1020
> Call Trace:
>  [<c015c0ef>] warn_slowpath_common+0x68/0x7d
>  [<c02b7e7d>] ? __jbd2_log_start_commit+0xba/0xcd
>  [<c015c177>] warn_slowpath_fmt+0x2b/0x2f
>  [<c02b7e7d>] __jbd2_log_start_commit+0xba/0xcd
>  [<c02b8075>] jbd2_log_start_commit+0x24/0x34
>  [<c0279ed5>] ext4_evict_inode+0x71/0x2e3
>  [<c021f0ec>] evict+0x94/0x135
>  [<c021f9aa>] iput+0x10a/0x110
>  [<c02b7836>] jbd2_journal_destroy+0x190/0x1ce
>  [<c0175284>] ? bit_waitqueue+0x50/0x50
>  [<c028d23f>] ext4_put_super+0x52/0x294
>  [<c020efe3>] generic_shutdown_super+0x48/0xb4
>  [<c020f071>] kill_block_super+0x22/0x60
>  [<c020f3e0>] deactivate_locked_super+0x22/0x49
>  [<c020f5d6>] deactivate_super+0x30/0x33
>  [<c0222795>] mntput_no_expire+0x107/0x10c
>  [<c02233a7>] sys_umount+0x2cf/0x2e0
>  [<c02233ca>] sys_oldumount+0x12/0x14
>  [<c08096b8>] syscall_call+0x7/0xb
> ---[ end trace 6a954cc790501c1f ]---
> jbd2_log_wait_commit: error: j_commit_request=-1289337090, tid=0
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> Cc: Jan Kara <jack@...e.cz>
> Cc: stable@...r.kernel.org
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

  I'll also push a similar fix to ext3.

								Honza
> ---
>  fs/ext4/inode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 15e0da1..0a6434c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -205,7 +205,8 @@ void ext4_evict_inode(struct inode *inode)
>  		 * don't use page cache.
>  		 */
>  		if (ext4_should_journal_data(inode) &&
> -		    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) {
> +		    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode)) &&
> +		    inode->i_ino != EXT4_JOURNAL_INO) {
>  			journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
>  			tid_t commit_tid = EXT4_I(inode)->i_datasync_tid;
>  
> -- 
> 1.7.12.rc0.22.gcdd159b
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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