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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Greg Edwards <gedwards@ddn.com>,
        Jens Axboe <axboe@kernel.dk>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.14 056/115] block: bvec_nr_vecs() returns value for wrong slab
Date:   Thu, 13 Sep 2018 15:31:16 +0200
Message-Id: <20180913131827.178534837@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Edwards <gedwards@ddn.com>

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

--- 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)