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>

3 files changed, 12 insertions, 39 deletions

diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index e4e841567459..aefb78e3cbf9 100644
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -208,31 +208,6 @@ void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios)
 EXPORT_SYMBOL_GPL(dm_cell_release);
 
 /*
- * There are a couple of places where we put a bio into a cell briefly
- * before taking it out again.  In these situations we know that no other
- * bio may be in the cell.  This function releases the cell, and also does
- * a sanity check.
- */
-static void __cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
-{
-        BUG_ON(cell->holder != bio);
-        BUG_ON(!bio_list_empty(&cell->bios));
-
-        __cell_release(cell, NULL);
-}
-
-void dm_cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
-{
-        unsigned long flags;
-        struct dm_bio_prison *prison = cell->prison;
-
-        spin_lock_irqsave(&prison->lock, flags);
-        __cell_release_singleton(cell, bio);
-        spin_unlock_irqrestore(&prison->lock, flags);
-}
-EXPORT_SYMBOL_GPL(dm_cell_release_singleton);
-
-/*
  * Sometimes we don't want the holder, just the additional bios.
  */
 static void __cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
diff --git a/drivers/md/dm-bio-prison.h b/drivers/md/dm-bio-prison.h
index 4e0ac376700a..53d1a7a84e2f 100644
--- a/drivers/md/dm-bio-prison.h
+++ b/drivers/md/dm-bio-prison.h
@@ -44,7 +44,6 @@ int dm_bio_detain(struct dm_bio_prison *prison, struct dm_cell_key *key,
                   struct bio *inmate, struct dm_bio_prison_cell **ref);
 
 void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios);
-void dm_cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio); // FIXME: bio arg not needed
 void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates);
 void dm_cell_error(struct dm_bio_prison_cell *cell);
 
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;
         }