dm: always allow one page in dm_merge_bvec

Some callers assume they can always add at least one page to an empty bio,
so dm_merge_bvec should not return 0 in this case: we'll reject the I/O
later after the bio is submitted.

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

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index bca448e11878..469cec54f371 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -837,10 +837,10 @@ static int dm_merge_bvec(struct request_queue *q,
         struct dm_table *map = dm_get_table(md);
         struct dm_target *ti;
         sector_t max_sectors;
-        int max_size;
+        int max_size = 0;
 
         if (unlikely(!map))
-                return 0;
+                goto out;
 
         ti = dm_table_find_target(map, bvm->bi_sector);
 
@@ -861,14 +861,15 @@ static int dm_merge_bvec(struct request_queue *q,
         if (max_size && ti->type->merge)
                 max_size = ti->type->merge(ti, bvm, biovec, max_size);
 
+        dm_table_put(map);
+
+out:
         /*
          * Always allow an entire first page
          */
         if (max_size <= biovec->bv_len && !(bvm->bi_size >> SECTOR_SHIFT))
                 max_size = biovec->bv_len;
 
-        dm_table_put(map);
-
         return max_size;
 }