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 <[email protected]>
---
 block/bio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 047c5dca6d90..ff94640bc734 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -156,7 +156,7 @@ static void bio_put_slab(struct bio_set *bs)
 
 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)
-- 
2.17.1

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