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

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

From: Lukas Czerner <lczer...@redhat.com>

commit 09869de57ed2728ae3c619803932a86cb0e2c4f8 upstream.

DM thinp already checks whether the discard_granularity of the data
device is a factor of the thin-pool block size.  But when using the
dm-thin-pool's discard passdown support, DM thinp was not selecting the
max of the underlying data device's discard_granularity and the
thin-pool's block size.

Update set_discard_limits() to set discard_granularity to the max of
these values.  This enables blkdev_issue_discard() to properly align the
discards that are sent to the DM thin device on a full block boundary.
As such each discard will now cover an entire DM thin-pool block and the
block will be reclaimed.

Reported-by: Zdenek Kabelac <zkabe...@redhat.com>
Signed-off-by: Lukas Czerner <lczer...@redhat.com>
Signed-off-by: Mike Snitzer <snit...@redhat.com>
Signed-off-by: Luis Henriques <luis.henriq...@canonical.com>
---
 drivers/md/dm-thin.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 316f8a9af93b..7dab6e605c88 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -2675,7 +2675,8 @@ static void set_discard_limits(struct pool_c *pt, struct 
queue_limits *limits)
         */
        if (pt->adjusted_pf.discard_passdown) {
                data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits;
-               limits->discard_granularity = data_limits->discard_granularity;
+               limits->discard_granularity = 
max(data_limits->discard_granularity,
+                                                 pool->sectors_per_block << 
SECTOR_SHIFT);
        } else
                limits->discard_granularity = pool->sectors_per_block << 
SECTOR_SHIFT;
 }
-- 
1.9.1

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