kmemtrace: trace kfree() calls with NULL or zero-length objects

Impact: also output kfree(NULL) entries

This patch moves the trace_kfree() calls before the ZERO_OR_NULL_PTR
check so that we can trace call-sites that call kfree() with NULL many
times which might be an indication of a bug.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
LKML-Reference: <1237971957.30175.18.camel@penberg-laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/mm/slub.c b/mm/slub.c
index a98078b..7ab54ec 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2792,6 +2792,8 @@
 	struct page *page;
 	void *object = (void *)x;
 
+	trace_kfree(_RET_IP_, x);
+
 	if (unlikely(ZERO_OR_NULL_PTR(x)))
 		return;
 
@@ -2802,8 +2804,6 @@
 		return;
 	}
 	slab_free(page->slab, page, object, _RET_IP_);
-
-	trace_kfree(_RET_IP_, x);
 }
 EXPORT_SYMBOL(kfree);