Commit cd6521d0 authored by Mikulas Patocka's avatar Mikulas Patocka
Browse files

dm: disable REQ_NOWAIT for flushes 



REQ_NOWAIT for flushes cannot be easily supported by device mapper
because it may allocate multiple bios and its impossible to undo if one
of those allocations wants to wait. So, this patch disables REQ_NOWAIT
flushes in device mapper and we always return EAGAIN.

Previously, the code accepted REQ_NOWAIT flushes, but the non-blocking
execution was not guaranteed.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
parent 6942348d

drivers/md/dm.c

+9 −0
Original line number Diff line number Diff line
@@ -1968,6 +1968,15 @@ static void dm_split_and_process_bio(struct mapped_device *md, 


	/* Only support nowait for normal IO */

	if (unlikely(bio->bi_opf & REQ_NOWAIT) && !is_abnormal) {

		/*

		 * Don't support NOWAIT for FLUSH because it may allocate

		 * multiple bios and there's no easy way how to undo the

		 * allocations.

		 */

		if (bio->bi_opf & REQ_PREFLUSH) {

			bio_wouldblock_error(bio);

			return;

		}

		io = alloc_io(md, bio, GFP_NOWAIT);

		if (unlikely(!io)) {

			/* Unable to do anything without dm_io. */