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[PATCH 9/9] blkdev: Fix up AIO+DIO+O_SYNC to do the sync part correctly

To: axboe@xxxxxxxxx, tytso@xxxxxxx, david@xxxxxxxxxxxxx, jmoyer@xxxxxxxxxx, bpm@xxxxxxx, viro@xxxxxxxxxxxxxxxxxx, jack@xxxxxxx
Subject: [PATCH 9/9] blkdev: Fix up AIO+DIO+O_SYNC to do the sync part correctly
From: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Date: Mon, 19 Nov 2012 23:51:15 -0800
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, hch@xxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20121120074116.24645.36369.stgit@xxxxxxxxxxxxxxxxxxx>
References: <20121120074116.24645.36369.stgit@xxxxxxxxxxxxxxxxxxx>
User-agent: StGit/0.15
When performing O_SYNC+AIO+DIO writes to block devices, use the DIO_SYNC_WRITES
flag so that flushes are issued /after/ the write completes, not before.

Note, however, that for block devices, the DIO setup code ensures that a flush
wq is attached to the superblock of the bdevfs filesystem, not the filesystem
that the device node happens to reside in.  This means that unlike regular
files, iocb->ki_filp->f_mapping->host->i_sb != inode->i_sb.  Therefore, adjust
Jeff's earlier patch to keep the pointer use consistent and avoid a NULL deref.

Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
 fs/block_dev.c |    5 +++--
 fs/direct-io.c |    3 ++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1a1e5e3..05ff33a 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -235,7 +235,8 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct 
iovec *iov,
        struct inode *inode = file->f_mapping->host;
        return __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iov, offset,
-                                   nr_segs, blkdev_get_blocks, NULL, NULL, 0);
+                                   nr_segs, blkdev_get_blocks, NULL, NULL,
+                                   DIO_SYNC_WRITES);
 int __sync_blockdev(struct block_device *bdev, int wait)
@@ -1631,7 +1632,7 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const struct 
iovec *iov,
        ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
-       if (ret > 0 || ret == -EIOCBQUEUED) {
+       if (ret > 0) {
                ssize_t err;
                err = generic_write_sync(file, pos, ret);
diff --git a/fs/direct-io.c b/fs/direct-io.c
index b7391d4..c626c43 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -258,7 +258,8 @@ void generic_dio_end_io(struct kiocb *iocb, loff_t offset, 
ssize_t bytes,
                work->ret = ret;
                work->offset = offset;
                work->len = bytes;
-               queue_work(inode->i_sb->s_dio_flush_wq, &work->work);
+               queue_work(iocb->ki_filp->f_mapping->host->i_sb->s_dio_flush_wq,
+                          &work->work);
        } else {
                aio_complete(iocb, ret, 0);

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