Re: 2.6.28 ext4, xen and lvm volume becomes ro after snapshot

From: Andreas Sundstrom
Date: Sat Dec 27 2008 - 04:20:12 EST


Theodore Tso wrote:
> On Fri, Dec 26, 2008 at 11:00:11PM +0100, Andreas Sundstrom wrote:
>> But I enabled debugfs and did
>> "echo 3 > /sys/kernel/debug/jbd2/jbd2-debug" and reproduced the problem
>> by taking a snapshot while the system was live.
>> I hope this had the same effect as your proposed change.
>
> Thanks, that was helpful. Can you try applying this patch, and let me
> know whether the printk triggers?

No problem

>
> What I'm guessing is going on is that on a native kernel, we get the
> ENOTSUPP error immediately when we call submit_bh(). However, with
> the Xen kernel, we aren't getting the error right away; we're either
> getting ENOTSUPP later on, when we call wait_on_buffer(). For ext3,
> this doesn't matter, since we call sync_dirty_buffer() which calls
> submit_bh() and wait_on_buffer() synchronously. But ext4 doesn't use
> sync_dirty_buffer(), instead calling submit_bh() and wait_on_buffer()
> separately.
>
> This patch should be able to confirm whether or not this supposition
> is correct.
>
> - Ted
>
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index bd1fad0..630196d 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -174,9 +174,16 @@ static int journal_wait_on_commit_record(struct buffer_head *bh)
>
> clear_buffer_dirty(bh);
> wait_on_buffer(bh);
> + if (buffer_eopnotsupp(bh)) {
> + printk("jbd2: journal_wait_on_commit_record: eopnotsupp\n");
> + ret = sync_dirty_buffer(bh);
> + printk("jbd2: sync_dirty_buffer returned %d\n", ret);
> + }
>
> - if (unlikely(!buffer_uptodate(bh)))
> + if (unlikely(!buffer_uptodate(bh))) {
> + printk("jbd2: journal_wait_on_commit_record: not uptodate\n");
> ret = -EIO;
> + }
> put_bh(bh); /* One for getblk() */
> jbd2_journal_put_journal_head(bh2jh(bh));
>

[ 44.546636] blkfront: xvda1: write barrier op failed

[ 44.546666] blkfront: xvda1: barriers disabled

[ 44.546686] end_request: I/O error, dev xvda1, sector 5256

[ 44.546710] end_request: I/O error, dev xvda1, sector 5256

[ 44.548228] jbd2: journal_wait_on_commit_record: eopnotsupp

[ 44.548251] jbd2: sync_dirty_buffer returned 0

[ 44.548270] jbd2: journal_wait_on_commit_record: not uptodate

[ 44.548293] Aborting journal on device xvda1:8.

More output here http://pastebin.com/m3694a25b
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/