From: Mike Snitzer The dm thin pool target claims to support the zeroing of discarded data areas. This turns out to be incorrect when processing discards that do not exactly cover a complete number of blocks, so the target must always set discard_zeroes_data_unsupported. The thin pool target will zero blocks when they are allocated if the skip_block_zeroing feature is not specified. The block layer may send a discard that only partly covers a block. If a thin pool block is partially discarded then there is no guarantee that the discarded data will get zeroed before it is accessed again. Due to this, thin devices cannot claim discards will always zero data. Signed-off-by: Mike Snitzer Signed-off-by: Joe Thornber Cc: stable@vger.kernel.org # 3.4+ Signed-off-by: Alasdair G Kergon --- drivers/md/dm-thin.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux/drivers/md/dm-thin.c =================================================================== --- linux.orig/drivers/md/dm-thin.c +++ linux/drivers/md/dm-thin.c @@ -2274,6 +2274,7 @@ static int pool_ctr(struct dm_target *ti * thin devices' discard limits consistent). */ ti->discards_supported = true; + ti->discard_zeroes_data_unsupported = true; } ti->private = pt; @@ -2745,7 +2746,6 @@ static void set_discard_limits(struct po * boundary is not sent to this target. */ limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT; - limits->discard_zeroes_data = pool->pf.zero_new_blocks; } static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)