mm/mempool.c: update the kmemleak stack trace for mempool allocations

When mempool_alloc() returns an existing pool object, kmemleak_alloc()
is no longer called and the stack trace corresponds to the original
object allocation.  This patch updates the kmemleak allocation stack
trace for such objects to make it more useful for debugging.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mempool.c

@@ -10,6 +10,7 @@
 
 #include <linux/mm.h>
 #include <linux/slab.h>
+#include <linux/kmemleak.h>
 #include <linux/export.h>
 #include <linux/mempool.h>
 #include <linux/blkdev.h>
@@ -222,6 +223,11 @@ void * mempool_alloc(mempool_t *pool, gfp_t gfp_mask)
 		spin_unlock_irqrestore(&pool->lock, flags);
 		/* paired with rmb in mempool_free(), read comment there */
 		smp_wmb();
+		/*
+		 * Update the allocation stack trace as this is more useful
+		 * for debugging.
+		 */
+		kmemleak_update_trace(element);
 		return element;
 	}