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Commit bd4aaf8f authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm: fix dm_merge_bvec regression on 32 bit systems 

A DM regression on 32 bit systems was reported against v4.2-rc3 here:
https://lkml.org/lkml/2015/7/29/401



Fix this by reverting both commit 1c220c69 ("dm: fix casting bug in
dm_merge_bvec()") and 148e51ba ("dm: improve documentation and code
clarity in dm_merge_bvec").  This combined revert is done to eliminate
the possibility of a partial revert in stable@ kernels.

In hindsight the correct fix, at the time 1c220c69 was applied to fix
the regression that 148e51ba introduced, should've been to simply revert
148e51ba.

Reported-by: default avatarJosh Boyer <jwboyer@fedoraproject.org>
Tested-by: default avatarAdam Williamson <awilliam@redhat.com>
Acked-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 3.19+
parent 795e633a

drivers/md/dm.c

+10 −17
Original line number Diff line number Diff line
@@ -1729,7 +1729,8 @@ static int dm_merge_bvec(struct request_queue *q, 
	struct mapped_device *md = q->queuedata;

	struct dm_table *map = dm_get_live_table_fast(md);

	struct dm_target *ti;

	sector_t max_sectors, max_size = 0;

	sector_t max_sectors;

	int max_size = 0;



	if (unlikely(!map))

		goto out;
@@ -1742,18 +1743,10 @@ static int dm_merge_bvec(struct request_queue *q, 
	 * Find maximum amount of I/O that won't need splitting

	 */

	max_sectors = min(max_io_len(bvm->bi_sector, ti),

			  (sector_t) queue_max_sectors(q));

			  (sector_t) BIO_MAX_SECTORS);

	max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size;



	/*

	 * FIXME: this stop-gap fix _must_ be cleaned up (by passing a sector_t

	 * to the targets' merge function since it holds sectors not bytes).

	 * Just doing this as an interim fix for stable@ because the more

	 * comprehensive cleanup of switching to sector_t will impact every

	 * DM target that implements a ->merge hook.

	 */

	if (max_size > INT_MAX)

		max_size = INT_MAX;

	if (max_size < 0)

		max_size = 0;



	/*

	 * merge_bvec_fn() returns number of bytes
@@ -1761,13 +1754,13 @@ static int dm_merge_bvec(struct request_queue *q, 
	 * max is precomputed maximal io size

	 */

	if (max_size && ti->type->merge)

		max_size = ti->type->merge(ti, bvm, biovec, (int) max_size);

		max_size = ti->type->merge(ti, bvm, biovec, max_size);

	/*

	 * If the target doesn't support merge method and some of the devices

	 * provided their merge_bvec method (we know this by looking for the

	 * max_hw_sectors that dm_set_device_limits may set), then we can't

	 * allow bios with multiple vector entries.  So always set max_size

	 * to 0, and the code below allows just one page.

	 * provided their merge_bvec method (we know this by looking at

	 * queue_max_hw_sectors), then we can't allow bios with multiple vector

	 * entries.  So always set max_size to 0, and the code below allows

	 * just one page.

	 */

	else if (queue_max_hw_sectors(q) <= PAGE_SIZE >> 9)

		max_size = 0;