[PATCH 4/9] xfs: honor the O_SYNC flag for aysnchronous direct I/O requests

Darrick J. Wong
2012-11-20T08:16:17Z

If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get
flushed after the write completion for AIOs. This patch attempts to fix
that problem by marking an I/O as requiring a cache flush in endio
processing, and then issuing the cache flush after any unwritten extent
conversion is done.

From: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
[darrick.wong@oracle.com: Rework patch to use per-mount workqueues]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/xfs_aops.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++-
fs/xfs/xfs_aops.h | 1 +
fs/xfs/xfs_mount.h | 1 +
fs/xfs/xfs_super.c | 8 ++++++++
4 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index e57e2da..9cebbb7 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -173,6 +173,24 @@ xfs_setfilesize(
}

/*
+ * In the case of synchronous, AIO, O_DIRECT writes, we need to flush
+ * the disk cache when the I/O is complete.
+ */
+STATIC bool
+xfs_ioend_needs_cache_flush(
+ struct xfs_ioend *ioend)
+{
+ struct xfs_inode *ip = XFS_I(ioend->io_inode);
+ struct xfs_mount *mp = ip->i_mount;
+
+ if (!(mp->m_flags & XFS_MOUNT_BARRIER))
+ return false;
+
+ return IS_SYNC(ioend->io_inode) ||
+ (ioend->io_iocb->ki_filp->f_flags & O_DSYNC);
+}
+
+/*
* Schedule IO completion handling on the final put of an ioend.
*
* If there is no work to do we might as well call it a day and free the
@@ -189,11 +207,30 @@ xfs_finish_ioend(
queue_work(mp->m_unwritten_workqueue, &ioend->io_work);
else if (ioend->io_append_trans)
queue_work(mp->m_data_workqueue, &ioend->io_work);
+ else if (ioend->io_needs_fsync)
+ queue_work(mp->m_aio_blkdev_flush_wq, &ioend->io_work);
else
xfs_destroy_ioend(ioend);
}
}

+STATIC int
+xfs_ioend_force_cache_flush(
+ xfs_ioend_t *ioend)
+{
+ struct xfs_inode *ip = XFS_I(ioend->io_inode);
+ struct xfs_mount *mp = ip->i_mount;
+ int err = 0;
+ int datasync;
+
+ datasync = !IS_SYNC(ioend->io_inode) &&
+ !(ioend->io_iocb->ki_filp->f_flags & __O_SYNC);
+ err = do_xfs_file_fsync(ip, mp, datasync);
+ xfs_destroy_ioend(ioend);
+ /* do_xfs_file_fsync returns -errno. our caller expects positive. */
+ return -err;
+}
+
/*
* IO write completion.
*/
@@ -250,12 +287,22 @@ xfs_end_io(
error = xfs_setfilesize(ioend);
if (error)
ioend->io_error = -error;
+ } else if (ioend->io_needs_fsync) {
+ error = xfs_ioend_force_cache_flush(ioend);
+ if (error && ioend->io_result > 0)
+ ioend->io_error = -error;
+ ioend->io_needs_fsync = 0;
} else {
ASSERT(!xfs_ioend_is_append(ioend));
}

done:
- xfs_destroy_ioend(ioend);
+ /* the honoring of O_SYNC has to be done last */
+ if (ioend->io_needs_fsync) {
+ atomic_inc(&ioend->io_remaining);
+ xfs_finish_ioend(ioend);
+ } else
+ xfs_destroy_ioend(ioend);
}

/*
@@ -292,6 +339,7 @@ xfs_alloc_ioend(
atomic_set(&ioend->io_remaining, 1);
ioend->io_isasync = 0;
ioend->io_isdirect = 0;
+ ioend->io_needs_fsync = 0;
ioend->io_error = 0;
ioend->io_list = NULL;
ioend->io_type = type;
@@ -1409,6 +1457,8 @@ xfs_end_io_direct_write(

if (is_async) {
ioend->io_isasync = 1;
+ if (xfs_ioend_needs_cache_flush(ioend))
+ ioend->io_needs_fsync = 1;
xfs_finish_ioend(ioend);
} else {
xfs_finish_ioend_sync(ioend);
diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
index c325abb..e48c7c2 100644
--- a/fs/xfs/xfs_aops.h
+++ b/fs/xfs/xfs_aops.h
@@ -47,6 +47,7 @@ typedef struct xfs_ioend {
atomic_t io_remaining; /* hold count */
unsigned int io_isasync : 1; /* needs aio_complete */
unsigned int io_isdirect : 1;/* direct I/O */
+ unsigned int io_needs_fsync : 1; /* aio+dio+o_sync */
struct inode *io_inode; /* file being written to */
struct buffer_head *io_buffer_head;/* buffer linked list head */
struct buffer_head *io_buffer_tail;/* buffer linked list tail */
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index deee09e..ecd3d2e 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -209,6 +209,7 @@ typedef struct xfs_mount {
struct workqueue_struct *m_data_workqueue;
struct workqueue_struct *m_unwritten_workqueue;
struct workqueue_struct *m_cil_workqueue;
+ struct workqueue_struct *m_aio_blkdev_flush_wq;
} xfs_mount_t;

/*
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 26a09bd..b05b557 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -863,8 +863,15 @@ xfs_init_mount_workqueues(
WQ_MEM_RECLAIM, 0, mp->m_fsname);
if (!mp->m_cil_workqueue)
goto out_destroy_unwritten;
+
+ mp->m_aio_blkdev_flush_wq = alloc_workqueue("xfs-aio-blkdev-flush/%s",
+ WQ_MEM_RECLAIM, 0, mp->m_fsname);
+ if (!mp->m_aio_blkdev_flush_wq)
+ goto out_destroy_cil_queue;
return 0;

+out_destroy_cil_queue:
+ destroy_workqueue(mp->m_cil_workqueue);
out_destroy_unwritten:
destroy_workqueue(mp->m_unwritten_workqueue);
out_destroy_data_iodone_queue:
@@ -877,6 +884,7 @@ STATIC void
xfs_destroy_mount_workqueues(
struct xfs_mount *mp)
{
+ destroy_workqueue(mp->m_aio_blkdev_flush_wq);
destroy_workqueue(mp->m_cil_workqueue);
destroy_workqueue(mp->m_data_workqueue);
destroy_workqueue(mp->m_unwritten_workqueue);