On Mon, May 1, 2023 at 12:15 PM Mike Snitzer [off-list ref] wrote:

On Wed, Apr 19 2023 at  8:48P -0400,
Sarthak Kukreti [off-list ref] wrote:

quoted

dm-thinpool uses the provision request to provision
blocks for a dm-thin device. dm-thinpool currently does not
pass through REQ_OP_PROVISION to underlying devices.

For shared blocks, provision requests will break sharing and copy the
contents of the entire block. Additionally, if 'skip_block_zeroing'
is not set, dm-thin will opt to zero out the entire range as a part
of provisioning.

Signed-off-by: Sarthak Kukreti <redacted>
---
 drivers/md/dm-thin.c | 73 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 68 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 2b13c949bd72..58d633f5c928 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c

@@ -1891,7 +1893,8 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,

      if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size) {
              break_sharing(tc, bio, block, &key, lookup_result, data_cell);
-             cell_defer_no_holder(tc, virt_cell);
+             if (bio_op(bio) != REQ_OP_PROVISION)
+                     cell_defer_no_holder(tc, virt_cell);

Can you please explain why cell_defer_no_holder() is skipped for REQ_OP_PROVISION here?

I recalled seeing a BUG in dm-prison-v1 if I allowed
cell_defer_no_holder() for REQ_OP_PROVISION, but from additional
testing, it looks like it was left behind from a cleanup in v4.
Dropped in v6.

Thanks
Sarthak

Thanks,
Mike