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jbd2: use GFP_NOFS for blkdev_issue_flush

RFC Applied Shaohua Li 4 participants 4 messages Apr 13, 2012 – Apr 24, 2012

Subsystems (2)
VFS Journalling layer for block devices (JBD2)
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Shaohua Li

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#0 lore raw

RFC 1/1 jbd2: use GFP_NOFS for blkdev_issue_flush

flush request is issued in transaction commit code path, so looks using GFP_KERNEL to allocate memory for flush request bio falls into the classic deadlock issue. I saw btrfs and dm get it right, but ext4, xfs and md are using GFP_KERNEL, which makes me confused. Hoping filesystem developers clarify.

Signed-off-by Shaohua Li <[email protected]>
---
 fs/jbd2/commit.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
fs/jbd2/commit.c +2 -2
Index: linux/fs/jbd2/commit.c
===================================================================
@@ -723,7 +723,7 @@ start_journal_io:
 	if (commit_transaction->t_need_data_flush &&
 	    (journal->j_fs_dev != journal->j_dev) &&
 	    (journal->j_flags & JBD2_BARRIER))
-		blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
+		blkdev_issue_flush(journal->j_fs_dev, GFP_NOFS, NULL);
 
 	/* Done it all: now write the commit record asynchronously. */
 	if (JBD2_HAS_INCOMPAT_FEATURE(journal,

@@ -859,7 +859,7 @@ wait_for_iobuf:
 	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
 				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
 	    journal->j_flags & JBD2_BARRIER) {
-		blkdev_issue_flush(journal->j_dev, GFP_KERNEL, NULL);
+		blkdev_issue_flush(journal->j_dev, GFP_NOFS, NULL);
 	}
 
 	if (err)
#1 lore raw
Quoted 6 lines · Shaohua Li

flush request is issued in transaction commit code path, so looks using GFP_KERNEL to allocate memory for flush request bio falls into the classic deadlock issue. I saw btrfs and dm get it right, but ext4, xfs and md are using GFP_KERNEL, which makes me confused. Hoping filesystem developers clarify.

Only one of the 5 calls XFS makes to blkdev_issue_flush() is questionable. Probably should use GFP_NOFS by default, though, so we don't trip over this problem...

Cheers,

Dave.

Signature · 2 lines
Dave Chinner
[email protected]
reviewer Reviewed-by on v1 1/1
#2 lore raw
In reply to Shaohua Li
Quoted 8 lines · Shaohua Li

flush request is issued in transaction commit code path, so looks using GFP_KERNEL to allocate memory for flush request bio falls into the classic deadlock issue. I saw btrfs and dm get it right, but ext4, xfs and md are using GFP_KERNEL, which makes me confused. Hoping filesystem developers clarify.

Signed-off-by Shaohua Li <[email protected]>

Yeah, ext4 (jbd2) should use GFP_NOFS since we are in a kjournald and
reclaim could possibly need to start a transaction thus blocking on kjournald. So you have my:

Reviewed-by Jan Kara <[email protected]>

Honza

Quoted 30 lines
---
 fs/jbd2/commit.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux/fs/jbd2/commit.c
===================================================================

fs/jbd2/commit.c +2 -3
@@ -723,7 +723,7 @@ start_journal_io:
 	if (commit_transaction->t_need_data_flush &&
 	    (journal->j_fs_dev != journal->j_dev) &&
 	    (journal->j_flags & JBD2_BARRIER))
-		blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);
+		blkdev_issue_flush(journal->j_fs_dev, GFP_NOFS, NULL);
 
 	/* Done it all: now write the commit record asynchronously. */
 	if (JBD2_HAS_INCOMPAT_FEATURE(journal,

@@ -859,7 +859,7 @@ wait_for_iobuf:
 	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
 				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
 	    journal->j_flags & JBD2_BARRIER) {
-		blkdev_issue_flush(journal->j_dev, GFP_KERNEL, NULL);
+		blkdev_issue_flush(journal->j_dev, GFP_NOFS, NULL);
 	}
 
 	if (err)
--

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Signature · 2 lines
Jan Kara <[email protected]>
SUSE Labs, CR
maintainer Applied
#3 lore raw
In reply to Shaohua Li
Quoted 8 lines · Shaohua Li

flush request is issued in transaction commit code path, so looks using GFP_KERNEL to allocate memory for flush request bio falls into the classic deadlock issue. I saw btrfs and dm get it right, but ext4, xfs and md are using GFP_KERNEL, which makes me confused. Hoping filesystem developers clarify.

Signed-off-by Shaohua Li <[email protected]>

Thanks, applied.

- Ted