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(-)
Index: linux/fs/jbd2/commit.c
===================================================================
--- linux.orig/fs/jbd2/commit.c 2012-04-13 09:57:51.785506925 +0800
+++ linux/fs/jbd2/commit.c 2012-04-13 09:58:29.585498773 +0800
@@ -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)
On Fri, Apr 13, 2012 at 10:27:35AM +0800, Shaohua Li wrote:
>
> 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.
--
Dave Chinner
[email protected]
On Fri 13-04-12 10:27:35, Shaohua Li wrote:
>
> 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
> ---
> fs/jbd2/commit.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux/fs/jbd2/commit.c
> ===================================================================
> --- linux.orig/fs/jbd2/commit.c 2012-04-13 09:57:51.785506925 +0800
> +++ linux/fs/jbd2/commit.c 2012-04-13 09:58:29.585498773 +0800
> @@ -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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--
Jan Kara <[email protected]>
SUSE Labs, CR
On Fri, Apr 13, 2012 at 10:27:35AM +0800, Shaohua Li wrote:
>
> 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