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

Darrick J. Wong
2012-11-20T08:19:49Z

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@oracle.com>
---
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,
percpu_down_read(&bdev->bd_block_size_semaphore);

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);
inode_dio_done(inode);