Patch "block: Do a full clone when splitting discard bios" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

block: Do a full clone when splitting discard bios

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
block-do-a-full-clone-when-splitting-discard-bios.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Martin K. Petersen" <[email protected]>
Date: Wed, 22 Jul 2015 07:57:12 -0400
Subject: block: Do a full clone when splitting discard bios

From: "Martin K. Petersen" <[email protected]>

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.

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

@@ -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;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/block-do-a-full-clone-when-splitting-discard-bios.patch queue-4.1/libata-fall-back-to-unqueued-read-log-ext-if-the-dma-variant-fails.patch queue-4.1/libata-expose-trim-capability-in-sysfs.patch queue-4.1/libata-do-not-blacklist-micron-m500dc.patch queue-4.1/libata-do-not-blacklist-m510dc.patch

Greg,

not sure what the status of your backlog queue is, but since I've not yet seen this queued for 3.14 just a note that it applies cleanly when you change the file paths from /block/ to /fs/ to accommodate the later move of bio.c.

IMHO this is important to prevent more md/fstrim damage. If it's on the pile then just ignore this. :)

thanks,
-h

No, I didn't realize that, thanks, I'll go do that change now and queue it up, thanks for letting me know.

greg k-h