slob: Check for NULL pointer before calling ctor()

rostedt · penberg · commit c1e854e924f3 · 2013-07-07T19:19:23.000+03:00
While doing some code inspection, I noticed that the slob constructor
method can be called with a NULL pointer. If memory is tight and slob
fails to allocate with slob_alloc() or slob_new_pages() it still calls
the ctor() method with a NULL pointer. Looking at the first ctor()
method I found, I noticed that it can not handle a NULL pointer (I'm
sure others probably can't either):

static void sighand_ctor(void *data)
{
        struct sighand_struct *sighand = data;

        spin_lock_init(&amp;sighand-&gt;siglock);
        init_waitqueue_head(&amp;sighand-&gt;signalfd_wqh);
}

The solution is to only call the ctor() method if allocation succeeded.

Acked-by: Christoph Lameter &lt;cl@linux.com&gt;
Signed-off-by: Steven Rostedt &lt;rostedt@goodmis.org&gt;
Signed-off-by: Pekka Enberg &lt;penberg@kernel.org&gt;
diff --git a/mm/slob.c b/mm/slob.c
@@ -554,7 +554,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
 					    flags, node);
 	}
 
-	if (c->ctor)
+	if (b && c->ctor)
 		c->ctor(b);
 
 	kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);

Original file line number	Diff line number	Diff line change
`@@ -554,7 +554,7 @@ void kmem_cache_alloc_node(struct kmem_cache c, gfp_t flags, int node)`
`554`	`554`	`flags, node);`
`555`	`555`	`}`
`556`	`556`
`557`		`- if (c->ctor)`
	`557`	`+ if (b && c->ctor)`
`558`	`558`	`c->ctor(b);`
`559`	`559`
`560`	`560`	`kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);`