linux-kernel - [PATCH 4.1 122/267] block: Do a full clone when splitting discard bios

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Message-Id: <20150731194005.755060058@linuxfoundation.org>
Date:	Fri, 31 Jul 2015 12:39:33 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Seunguk Shin <seunguk.shin@...sung.com>,
	Jens Axboe <axboe@...com>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Christoph Hellwig <hch@....de>
Subject: [PATCH 4.1 122/267] block: Do a full clone when splitting discard bios

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Martin K. Petersen" <martin.petersen@...cle.com>

commit f3f5da624e0a891c34d8cd513c57f1d9b0c7dadc upstream.

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

Commit 20d0189b1012 "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@...cle.com>
Reported-by: Seunguk Shin <seunguk.shin@...sung.com>
Tested-by: Seunguk Shin <seunguk.shin@...sung.com>
Cc: Seunguk Shin <seunguk.shin@...sung.com>
Cc: Jens Axboe <axboe@...com>
Cc: Kent Overstreet <kent.overstreet@...il.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/bio.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

--- a/block/bio.c
+++ b/block/bio.c
@@ -1814,8 +1814,9 @@ EXPORT_SYMBOL(bio_endio_nodec);
  * 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)
@@ -1825,7 +1826,15 @@ struct bio *bio_split(struct bio *bio, i
 	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;

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