Commit f3f5da62 authored Jul 22, 2015 by Martin K. Petersen Committed by Jens Axboe Jul 23, 2015

block: Do a full clone when splitting discard bios



This fixes a data corruption bug when using discard on top of MD linear,
raid0 and raid10 personalities.

Commit 20d0189b "block: Introduce new bio_split()" permits sharing
the bio_vec between the two resulting bios. That is fine for read/write
requests where the bio_vec is immutable. For discards, however, we need
to be able to attach a payload and update the bio_vec so the page can
get mapped to a scatterlist entry. Therefore the bio_vec can not be
shared when splitting discards and we must do a full clone.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Reported-by: Seunguk Shin <seunguk.shin@samsung.com>
Tested-by: Seunguk Shin <seunguk.shin@samsung.com>
Cc: Seunguk Shin <seunguk.shin@samsung.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: <stable@vger.kernel.org> # v3.14+
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 5aa2a96b

block/bio.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -1831,8 +1831,9 @@ EXPORT_SYMBOL(bio_endio);
		* Allocates and returns a new bio which represents @sectors from the start of
		* @bio, and updates @bio to represent the remaining sectors.
		*
		* The newly allocated bio will point to @bio's bi_io_vec; it is the caller's
		* responsibility to ensure that @bio is not freed before the split.
		* Unless this is a discard request the newly allocated bio will point
		* to @bio's bi_io_vec; it is the caller's responsibility to ensure that
		* @bio is not freed before the split.
		*/
		struct bio bio_split(struct bio bio, int sectors,
		gfp_t gfp, struct bio_set *bs)
		@@ -1842,7 +1843,15 @@ struct bio bio_split(struct bio bio, int sectors,
		BUG_ON(sectors <= 0);
		BUG_ON(sectors >= bio_sectors(bio));

		/*
		* Discards need a mutable bio_vec to accommodate the payload
		* required by the DSM TRIM and UNMAP commands.
		*/
		if (bio->bi_rw & REQ_DISCARD)
		split = bio_clone_bioset(bio, gfp, bs);
		else
		split = bio_clone_fast(bio, gfp, bs);

		if (!split)
		return NULL;