linux-kernel - [PATCH 5.1 345/371] xfs: abort unaligned nowait directio early

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Date:   Wed, 24 Jul 2019 21:21:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Chinner <david@...morbit.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Brian Foster <bfoster@...hat.com>,
        Dave Chinner <dchinner@...hat.com>,
        Christoph Hellwig <hch@....de>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.1 345/371] xfs: abort unaligned nowait directio early

[ Upstream commit 1fdeaea4d92c69fb9f871a787af6ad00f32eeea7 ]

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@...morbit.com>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Reviewed-by: Brian Foster <bfoster@...hat.com>
Reviewed-by: Dave Chinner <dchinner@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 a7ceae90110e..76748255f843 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);
-- 
2.20.1