Commit ebf00be3 authored by Andreas Gruenbacher's avatar Andreas Gruenbacher Committed by Darrick J. Wong
Browse files

iomap: complete partial direct I/O writes synchronously 



According to xfstest generic/240, applications seem to expect direct I/O
writes to either complete as a whole or to fail; short direct I/O writes
are apparently not appreciated.  This means that when only part of an
asynchronous direct I/O write succeeds, we can either fail the entire
write, or we can wait for the partial write to complete and retry the
remaining write as buffered I/O.  The old __blockdev_direct_IO helper
has code for waiting for partial writes to complete; the new
iomap_dio_rw iomap helper does not.

The above mentioned fallback mode is needed for gfs2, which doesn't
allow block allocations under direct I/O to avoid taking cluster-wide
exclusive locks.  As a consequence, an asynchronous direct I/O write to
a file range that contains a hole will result in a short write.  In that
case, wait for the short write to complete to allow gfs2 to recover.

Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent 3d7b6b21

fs/iomap.c

+11 −10
Original line number Diff line number Diff line
@@ -811,6 +811,7 @@ struct iomap_dio { 
	atomic_t		ref;

	unsigned		flags;

	int			error;

	bool			wait_for_completion;



	union {

		/* used during submission and for synchronous completion: */
@@ -914,9 +915,8 @@ static void iomap_dio_bio_end_io(struct bio *bio) 
		iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status));



	if (atomic_dec_and_test(&dio->ref)) {

		if (is_sync_kiocb(dio->iocb)) {

		if (dio->wait_for_completion) {

			struct task_struct *waiter = dio->submit.waiter;



			WRITE_ONCE(dio->submit.waiter, NULL);

			wake_up_process(waiter);

		} else if (dio->flags & IOMAP_DIO_WRITE) {
@@ -1131,13 +1131,12 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, 
	dio->end_io = end_io;

	dio->error = 0;

	dio->flags = 0;

	dio->wait_for_completion = is_sync_kiocb(iocb);



	dio->submit.iter = iter;

	if (is_sync_kiocb(iocb)) {

	dio->submit.waiter = current;

	dio->submit.cookie = BLK_QC_T_NONE;

	dio->submit.last_queue = NULL;

	}



	if (iov_iter_rw(iter) == READ) {

		if (pos >= dio->i_size)
@@ -1187,7 +1186,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, 
		dio_warn_stale_pagecache(iocb->ki_filp);

	ret = 0;



	if (iov_iter_rw(iter) == WRITE && !is_sync_kiocb(iocb) &&

	if (iov_iter_rw(iter) == WRITE && !dio->wait_for_completion &&

	    !inode->i_sb->s_dio_done_wq) {

		ret = sb_init_dio_done_wq(inode->i_sb);

		if (ret < 0)
@@ -1202,8 +1201,10 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, 
				iomap_dio_actor);

		if (ret <= 0) {

			/* magic error code to fall back to buffered I/O */

			if (ret == -ENOTBLK)

			if (ret == -ENOTBLK) {

				dio->wait_for_completion = true;

				ret = 0;

			}

			break;

		}

		pos += ret;
@@ -1224,7 +1225,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, 
		dio->flags &= ~IOMAP_DIO_NEED_SYNC;



	if (!atomic_dec_and_test(&dio->ref)) {

		if (!is_sync_kiocb(iocb))

		if (!dio->wait_for_completion)

			return -EIOCBQUEUED;



		for (;;) {

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