On Mon, 14 Sep 2015, Mike Snitzer wrote:

On Mon, Sep 14 2015 at  9:46am -0400,
Mikulas Patocka [off-list ref] wrote:

quoted

On Sun, 13 Sep 2015, Julia Lawall wrote:

quoted

Remove unneeded NULL test.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>

@@ expression x; @@
-if (x != NULL)
  \(kmem_cache_destroy\|mempool_destroy\|dma_pool_destroy\)(x);

// </smpl>

Signed-off-by: Julia Lawall <redacted>

---
 drivers/md/dm-bufio.c              |    3 +--
 drivers/md/dm-cache-target.c       |    3 +--
 drivers/md/dm-crypt.c              |    6 ++----
 drivers/md/dm-io.c                 |    3 +--
 drivers/md/dm-log-userspace-base.c |    3 +--
 drivers/md/dm-region-hash.c        |    4 +---
 drivers/md/dm.c                    |   13 ++++---------
 7 files changed, 11 insertions(+), 24 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 83cc52e..8ad39b6 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c

@@ -1864,8 +1864,7 @@ static void __exit dm_bufio_exit(void)
 	for (i = 0; i < ARRAY_SIZE(dm_bufio_caches); i++) {
 		struct kmem_cache *kc = dm_bufio_caches[i];
 
-		if (kc)
-			kmem_cache_destroy(kc);
+		kmem_cache_destroy(kc);
 	}

The variable here can be NULL. I don't know how did you conclude that it 
cannot. It seems that you didn't test the patch, if you did, you'd hit 
NULL pointer dereference here.

kmem_cache_destroy(), mempool_destroy(), etc all check for NULL and just
return.  So there is no need for the callers to check for NULL too.

Mike

I see. It was recent change that I missed.

Mikulas