dm raid1: set discard_zeroes_data_unsupported

We can't guarantee that REQ_DISCARD on dm-mirror zeroes the data even if
the underlying disks support zero on discard.  So this patch sets
ti->discard_zeroes_data_unsupported.

For example, if the mirror is in the process of resynchronizing, it may
happen that kcopyd reads a piece of data, then discard is sent on the
same area and then kcopyd writes the piece of data to another leg.
Consequently, the data is not zeroed.

The flag was made available by commit 983c7db347db8ce2d8453fd1d89b7a4bb6920d56
(dm crypt: always disable discard_zeroes_data).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index ea16984c0f082536643a733b6e8b9f9026bde390..b58b7a33914abd721e3508835a61afd699221dbf 100644 (file)
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -1084,6 +1084,7 @@ static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
        ti->split_io = dm_rh_get_region_size(ms->rh);
        ti->num_flush_requests = 1;
        ti->num_discard_requests = 1;
+       ti->discard_zeroes_data_unsupported = 1;
 
        ms->kmirrord_wq = alloc_workqueue("kmirrord",
                                          WQ_NON_REENTRANT | WQ_MEM_RECLAIM, 0);