Ocfs2 devel - Jan 2018 - [PATCH v2] ocfs2: return error when we attempt to access a dirty bh in jbd2

We should not reuse the dirty bh in jbd2 directly due to the following
situation:

1. When removing extent rec, we will dirty the bhs of extent rec and
   truncate log at the same time, and hand them over to jbd2.
2. The bhs are submitted to jbd2 area successfully.
3. The write-back thread of device help flush the bhs to disk but
   encounter write error due to abnormal storage link.
4. After a while the storage link become normal. Truncate log flush
   worker triggered by the next space reclaiming found the dirty bh of
   truncate log and clear its 'BH_Write_EIO' and then set it uptodate in
   __ocfs2_journal_access():

ocfs2_truncate_log_worker
  ocfs2_flush_truncate_log
    __ocfs2_flush_truncate_log
      ocfs2_replay_truncate_records
        ocfs2_journal_access_di
          __ocfs2_journal_access // here we clear io_error and set
'tl_bh' uptodata.

5. Then jbd2 will flush the bh of truncate log to disk, but the bh of
   extent rec is still in error state, and unfortunately nobody will
   take care of it.
6. At last the space of extent rec was not reduced, but truncate log
   flush worker have given it back to globalalloc. That will cause
   duplicate cluster problem which could be identified by fsck.ocfs2.

Sadlly we can hardly revert this but set fs read-only in case of
ruining atomicity and consistency of space reclaim.

Fixes: acf8fdbe6afb ("ocfs2: do not BUG if buffer not uptodate in
__ocfs2_journal_access")

Signed-off-by: Jun Piao <piaojun at huawei.com>
Reviewed-by: Yiwen Jiang <jiangyiwen at huawei.com>
---
 fs/ocfs2/journal.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 11 deletions(-)

diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
index 3630443..4c5661c 100644
--- a/fs/ocfs2/journal.c
+++ b/fs/ocfs2/journal.c
@@ -666,23 +666,50 @@ static int __ocfs2_journal_access(handle_t *handle,
 	/* we can safely remove this assertion after testing. */
 	if (!buffer_uptodate(bh)) {
 		mlog(ML_ERROR, "giving me a buffer that's not uptodate!\n");
-		mlog(ML_ERROR, "b_blocknr=%llu\n",
-		     (unsigned long long)bh->b_blocknr);
+		mlog(ML_ERROR, "b_blocknr=%llu, b_state=0x%lx\n",
+		     (unsigned long long)bh->b_blocknr, bh->b_state);

 		lock_buffer(bh);
 		/*
-		 * A previous attempt to write this buffer head failed.
-		 * Nothing we can do but to retry the write and hope for
-		 * the best.
+		 * We should not reuse the dirty bh directly due to the
+		 * following situation:
+		 *
+		 * 1. When removing extent rec, we will dirty the bhs of
+		 *    extent rec and truncate log at the same time, and
+		 *    hand them over to jbd2.
+		 * 2. The bhs are submitted to jbd2 area successfully.
+		 * 3. The write-back thread of device help flush the bhs
+		 *    to disk but encounter write error due to abnormal
+		 *    storage link.
+		 * 4. After a while the storage link become normal.
+		 *    Truncate log flush worker triggered by the next
+		 *    space reclaiming found the dirty bh of truncate log
+		 *    and clear its 'BH_Write_EIO' and then set it uptodate
+		 *    in __ocfs2_journal_access():
+		 *
+		 *    ocfs2_truncate_log_worker
+		 *      ocfs2_flush_truncate_log
+		 *        __ocfs2_flush_truncate_log
+		 *          ocfs2_replay_truncate_records
+		 *            ocfs2_journal_access_di
+		 *              __ocfs2_journal_access
+		 *
+		 * 5. Then jbd2 will flush the bh of truncate log to disk,
+		 *    but the bh of extent rec is still in error state, and
+		 *    unfortunately nobody will take care of it.
+		 * 6. At last the space of extent rec was not reduced,
+		 *    but truncate log flush worker have given it back to
+		 *    globalalloc. That will cause duplicate cluster problem
+		 *    which could be identified by fsck.ocfs2.
+		 *
+		 * Sadlly we can hardly revert this but set fs read-only
+		 * in case of ruining atomicity and consistency of space
+		 * reclaim.
 		 */
 		if (buffer_write_io_error(bh) && !buffer_uptodate(bh)) {
-			clear_buffer_write_io_error(bh);
-			set_buffer_uptodate(bh);
-		}
-
-		if (!buffer_uptodate(bh)) {
 			unlock_buffer(bh);
-			return -EIO;
+			return ocfs2_error(osb->sb, "A previous attempt to "
+					"write this buffer head failed\n");
 		}
 		unlock_buffer(bh);
 	}
--

Hi Jun,

On 2018/1/27 16:28, piaojun wrote:
> We should not reuse the dirty bh in jbd2 directly due to the following
> situation:
> 
> 1. When removing extent rec, we will dirty the bhs of extent rec and
>     truncate log at the same time, and hand them over to jbd2.
> 2. The bhs are submitted to jbd2 area successfully.
> 3. The write-back thread of device help flush the bhs to disk but
>     encounter write error due to abnormal storage link.
> 4. After a while the storage link become normal. Truncate log flush
>     worker triggered by the next space reclaiming found the dirty bh of
>     truncate log and clear its 'BH_Write_EIO' and then set it
uptodate in
>     __ocfs2_journal_access():
> 
> ocfs2_truncate_log_worker
>    ocfs2_flush_truncate_log
>      __ocfs2_flush_truncate_log
>        ocfs2_replay_truncate_records
>          ocfs2_journal_access_di
>            __ocfs2_journal_access // here we clear io_error and set
'tl_bh' uptodata.
> 
> 5. Then jbd2 will flush the bh of truncate log to disk, but the bh of
>     extent rec is still in error state, and unfortunately nobody will
>     take care of it.
> 6. At last the space of extent rec was not reduced, but truncate log
>     flush worker have given it back to globalalloc. That will cause
>     duplicate cluster problem which could be identified by fsck.ocfs2.
> 
> Sadlly we can hardly revert this but set fs read-only in case of
> ruining atomicity and consistency of space reclaim.
> 
> Fixes: acf8fdbe6afb ("ocfs2: do not BUG if buffer not uptodate in
__ocfs2_journal_access")
> 
> Signed-off-by: Jun Piao <piaojun at huawei.com>
> Reviewed-by: Yiwen Jiang <jiangyiwen at huawei.com>
> ---
>   fs/ocfs2/journal.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
>   1 file changed, 38 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
> index 3630443..4c5661c 100644
> --- a/fs/ocfs2/journal.c
> +++ b/fs/ocfs2/journal.c
> @@ -666,23 +666,50 @@ static int __ocfs2_journal_access(handle_t *handle,
>   	/* we can safely remove this assertion after testing. */
>   	if (!buffer_uptodate(bh)) {
>   		mlog(ML_ERROR, "giving me a buffer that's not
uptodate!\n");
> -		mlog(ML_ERROR, "b_blocknr=%llu\n",
> -		     (unsigned long long)bh->b_blocknr);
> +		mlog(ML_ERROR, "b_blocknr=%llu, b_state=0x%lx\n",
> +		     (unsigned long long)bh->b_blocknr, bh->b_state);
> 
>   		lock_buffer(bh);
>   		/*
> -		 * A previous attempt to write this buffer head failed.
> -		 * Nothing we can do but to retry the write and hope for
> -		 * the best.
> +		 * We should not reuse the dirty bh directly due to the
> +		 * following situation:
> +		 *
> +		 * 1. When removing extent rec, we will dirty the bhs of
> +		 *    extent rec and truncate log at the same time, and
> +		 *    hand them over to jbd2.
> +		 * 2. The bhs are submitted to jbd2 area successfully.
> +		 * 3. The write-back thread of device help flush the bhs
> +		 *    to disk but encounter write error due to abnormal
> +		 *    storage link.
> +		 * 4. After a while the storage link become normal.
> +		 *    Truncate log flush worker triggered by the next
> +		 *    space reclaiming found the dirty bh of truncate log
> +		 *    and clear its 'BH_Write_EIO' and then set it uptodate
> +		 *    in __ocfs2_journal_access():
> +		 *
> +		 *    ocfs2_truncate_log_worker
> +		 *      ocfs2_flush_truncate_log
> +		 *        __ocfs2_flush_truncate_log
> +		 *          ocfs2_replay_truncate_records
> +		 *            ocfs2_journal_access_di
> +		 *              __ocfs2_journal_access
> +		 *
> +		 * 5. Then jbd2 will flush the bh of truncate log to disk,
> +		 *    but the bh of extent rec is still in error state, and
> +		 *    unfortunately nobody will take care of it.
> +		 * 6. At last the space of extent rec was not reduced,
> +		 *    but truncate log flush worker have given it back to
> +		 *    globalalloc. That will cause duplicate cluster problem
> +		 *    which could be identified by fsck.ocfs2.
> +		 *
> +		 * Sadlly we can hardly revert this but set fs read-only
> +		 * in case of ruining atomicity and consistency of space
> +		 * reclaim.
>   		 */
It's tons of comments here and it seems the same with what's in change
log.
Must we add them here?
Besides, the scenario the comment is describing is not a common case.
I think the issue will also cause some other metadata inconsistency.
So the comments will make maintainers puzzle afterwards.
I suggest to simplify it like below, for your reference:

A previous transaction with a couple buffer heads fails checkpoint, so all those
buffer heads are marked IO_ERROR.
For current transaction, a buffer head is shared with the previous one with
IO_ERROR.
We can't just clear IO_ERROR and continue ,since other buffer heads are not
written to disk yet.
Above case will cause metadata inconsistency.
Just return -EORFS here and abort journal to avoid damage file system.

Thanks,
Changwei
>   		if (buffer_write_io_error(bh) && !buffer_uptodate(bh)) {
> -			clear_buffer_write_io_error(bh);
> -			set_buffer_uptodate(bh);
> -		}
> -
> -		if (!buffer_uptodate(bh)) {
>   			unlock_buffer(bh);
> -			return -EIO;
> +			return ocfs2_error(osb->sb, "A previous attempt to "
> +					"write this buffer head failed\n");
>   		}
>   		unlock_buffer(bh);
>   	}
>