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 20d0189 "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 <[email protected]> Reported-by: Seunguk Shin <[email protected]> Tested-by: Seunguk Shin <[email protected]> Cc: Seunguk Shin <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Kent Overstreet <[email protected]> Cc: <[email protected]> # v3.14+ Reviewed-by: Christoph Hellwig <[email protected]> Signed-off-by: Jens Axboe <[email protected]>
modi0012 · Jul 23, 2015 · f3f5da6 · f3f5da6
1 parent 5aa2a96
commit f3f5da6
Showing 1 changed file with 12 additions and 3 deletions.
diff --git a/block/bio.c b/block/bio.c
@@ -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));
 
-	split = bio_clone_fast(bio, gfp, bs);
+	/*
+	 * 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;