dm thin: replace dm_cell_release_singleton with cell_defer_except

Change existing users of the function dm_cell_release_singleton to share
cell_defer_except instead, and then remove the now-unused function.

Everywhere that calls dm_cell_release_singleton, the bio in question
is the holder of the cell.

If there are no non-holder entries in the cell then cell_defer_except
behaves exactly like dm_cell_release_singleton.  Conversely, if there
*are* non-holder entries then dm_cell_release_singleton must not be used
because those entries would need to be deferred.

Consequently, it is safe to replace use of dm_cell_release_singleton
with cell_defer_except.

This patch is a pre-requisite for "dm thin: fix race between
simultaneous io and discards to same block".

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 12 insertions, 13 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 058acf3a5ba7..25dfd2311a61 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -513,8 +513,7 @@ static void cell_defer(struct thin_c *tc, struct dm_bio_prison_cell *cell,
 }
 
 /*
- * Same as cell_defer above, except it omits one particular detainee,
- * a write bio that covers the block and has already been processed.
+ * Same as cell_defer except it omits the original holder of the cell.
  */
 static void cell_defer_except(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
@@ -936,7 +935,7 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
                  */
                 build_data_key(tc->td, lookup_result.block, &key2);
                 if (dm_bio_detain(tc->pool->prison, &key2, bio, &cell2)) {
-                        dm_cell_release_singleton(cell, bio);
+                        cell_defer_except(tc, cell);
                         break;
                 }
 
@@ -967,8 +966,8 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
                          * a block boundary.  So we submit the discard of a
                          * partial block appropriately.
                          */
-                        dm_cell_release_singleton(cell, bio);
-                        dm_cell_release_singleton(cell2, bio);
+                        cell_defer_except(tc, cell);
+                        cell_defer_except(tc, cell2);
                         if ((!lookup_result.shared) && pool->pf.discard_passdown)
                                 remap_and_issue(tc, bio, lookup_result.block);
                         else
@@ -980,13 +979,13 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
                 /*
                  * It isn't provisioned, just forget it.
                  */
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
                 bio_endio(bio, 0);
                 break;
 
         default:
                 DMERR("discard: find block unexpectedly returned %d", r);
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
                 bio_io_error(bio);
                 break;
         }
@@ -1041,7 +1040,7 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
 
                 h->shared_read_entry = dm_deferred_entry_inc(pool->shared_read_ds);
 
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
                 remap_and_issue(tc, bio, lookup_result->block);
         }
 }
@@ -1056,7 +1055,7 @@ static void provision_block(struct thin_c *tc, struct bio *bio, dm_block_t block
          * Remap empty bios (flushes) immediately, without provisioning.
          */
         if (!bio->bi_size) {
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
                 remap_and_issue(tc, bio, 0);
                 return;
         }
@@ -1066,7 +1065,7 @@ static void provision_block(struct thin_c *tc, struct bio *bio, dm_block_t block
          */
         if (bio_data_dir(bio) == READ) {
                 zero_fill_bio(bio);
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
                 bio_endio(bio, 0);
                 return;
         }
@@ -1120,7 +1119,7 @@ static void process_bio(struct thin_c *tc, struct bio *bio)
                  * TODO: this will probably have to change when discard goes
                  * back in.
                  */
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
 
                 if (lookup_result.shared)
                         process_shared_bio(tc, bio, block, &lookup_result);
@@ -1130,7 +1129,7 @@ static void process_bio(struct thin_c *tc, struct bio *bio)
 
         case -ENODATA:
                 if (bio_data_dir(bio) == READ && tc->origin_dev) {
-                        dm_cell_release_singleton(cell, bio);
+                        cell_defer_except(tc, cell);
                         remap_to_origin_and_issue(tc, bio);
                 } else
                         provision_block(tc, bio, block, cell);
@@ -1138,7 +1137,7 @@ static void process_bio(struct thin_c *tc, struct bio *bio)
 
         default:
                 DMERR("dm_thin_find_block() failed, error = %d", r);
-                dm_cell_release_singleton(cell, bio);
+                cell_defer_except(tc, cell);
                 bio_io_error(bio);
                 break;
         }