block: bvec_nr_vecs() returns value for wrong slab

BugLink: https://bugs.launchpad.net/bugs/1835972
[ Upstream commit d6c02a9beb67f13d5f14f23e72fa9981e8b84477 ]

In commit ed996a52c868 ("block: simplify and cleanup bvec pool
handling"), the value of the slab index is incremented by one in
bvec_alloc() after the allocation is done to indicate an index value of
0 does not need to be later freed.

bvec_nr_vecs() was not updated accordingly, and thus returns the wrong
value.  Decrement idx before performing the lookup.

Fixes: ed996a52c868 ("block: simplify and cleanup bvec pool handling")
Signed-off-by: Greg Edwards <gedwards@ddn.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/block/bio.c b/block/bio.c
index f411d634f62aef3c6e9e94ce1d09ff3bb6755069..66a7feb5414db13522c571ef67861d32d8975c4b 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -156,7 +156,7 @@ out:
 
 unsigned int bvec_nr_vecs(unsigned short idx)
 {
-       return bvec_slabs[idx].nr_vecs;
+       return bvec_slabs[--idx].nr_vecs;
 }
 
 void bvec_free(mempool_t *pool, struct bio_vec *bv, unsigned int idx)