[PATCH] xfs: abort unaligned nowait directio early

[PATCH] xfs: abort unaligned nowait directio early

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

Dave Chinner noticed that xfs_file_dio_aio_write returns EAGAIN without
dropping the IOLOCK when its deciding not to wait, which means that we
leak the IOLOCK there.  Since we now make unaligned directio always
wait, we have the opportunity to bail out before trying to take the
lock, which should reduce the overhead of this never-gonna-work case
considerably while also solving the dropped lock problem.

Reported-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/xfs_file.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index cdcc75735521..3a45e3b0efa7 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -517,6 +517,9 @@ xfs_file_dio_aio_write(
 	}
 
 	if (iocb->ki_flags & IOCB_NOWAIT) {
+		/* unaligned dio always waits, bail */
+		if (unaligned_io)
+			return -EAGAIN;
 		if (!xfs_ilock_nowait(ip, iolock))
 			return -EAGAIN;
 	} else {
@@ -536,9 +539,6 @@ xfs_file_dio_aio_write(
 	 * xfs_file_aio_write_checks() for other reasons.
 	 */
 	if (unaligned_io) {
-		/* unaligned dio always waits, bail */
-		if (iocb->ki_flags & IOCB_NOWAIT)
-			return -EAGAIN;
 		inode_dio_wait(inode);
 	} else if (iolock == XFS_IOLOCK_EXCL) {
 		xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);

Re: [PATCH] xfs: abort unaligned nowait directio early

[Brian Foster]

On Wed, Apr 17, 2019 at 07:40:06AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Dave Chinner noticed that xfs_file_dio_aio_write returns EAGAIN without
> dropping the IOLOCK when its deciding not to wait, which means that we
> leak the IOLOCK there.  Since we now make unaligned directio always
> wait, we have the opportunity to bail out before trying to take the
> lock, which should reduce the overhead of this never-gonna-work case
> considerably while also solving the dropped lock problem.
> 
> Reported-by: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/xfs_file.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index cdcc75735521..3a45e3b0efa7 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -517,6 +517,9 @@ xfs_file_dio_aio_write(
>  	}
>  
>  	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		/* unaligned dio always waits, bail */
> +		if (unaligned_io)
> +			return -EAGAIN;
>  		if (!xfs_ilock_nowait(ip, iolock))
>  			return -EAGAIN;
>  	} else {
> @@ -536,9 +539,6 @@ xfs_file_dio_aio_write(
>  	 * xfs_file_aio_write_checks() for other reasons.
>  	 */
>  	if (unaligned_io) {
> -		/* unaligned dio always waits, bail */
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> -			return -EAGAIN;
>  		inode_dio_wait(inode);
>  	} else if (iolock == XFS_IOLOCK_EXCL) {
>  		xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);

Re: [PATCH] xfs: abort unaligned nowait directio early

[Dave Chinner]

On Wed, Apr 17, 2019 at 07:40:06AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Dave Chinner noticed that xfs_file_dio_aio_write returns EAGAIN without
> dropping the IOLOCK when its deciding not to wait, which means that we
> leak the IOLOCK there.  Since we now make unaligned directio always
> wait, we have the opportunity to bail out before trying to take the
> lock, which should reduce the overhead of this never-gonna-work case
> considerably while also solving the dropped lock problem.
> 
> Reported-by: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Looks good.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH] xfs: abort unaligned nowait directio early

[Christoph Hellwig]

On Wed, Apr 17, 2019 at 07:40:06AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Dave Chinner noticed that xfs_file_dio_aio_write returns EAGAIN without
> dropping the IOLOCK when its deciding not to wait, which means that we
> leak the IOLOCK there.  Since we now make unaligned directio always
> wait, we have the opportunity to bail out before trying to take the
> lock, which should reduce the overhead of this never-gonna-work case
> considerably while also solving the dropped lock problem.
> 
> Reported-by: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>