mm/slab_common: allow NULL cache pointer in kmem_cache_destroy()

kmem_cache_destroy() does not tolerate a NULL kmem_cache pointer argument
and performs a NULL-pointer dereference.  This requires additional
attention and effort from developers/reviewers and forces all
kmem_cache_destroy() callers (200+ as of 4.1) to do a NULL check

    if (cache)
        kmem_cache_destroy(cache);

Or, otherwise, be invalid kmem_cache_destroy() users.

Tweak kmem_cache_destroy() and NULL-check the pointer there.

Proposed by Andrew Morton.

Link: https://lkml.org/lkml/2015/6/8/583
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index c26829f..bde04a6 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -640,6 +640,9 @@ void kmem_cache_destroy(struct kmem_cache *s)
        bool need_rcu_barrier = false;
        bool busy = false;
 
+       if (unlikely(!s))
+               return;
+
        BUG_ON(!is_root_cache(s));
 
        get_online_cpus();