On Thu, 17 Jan 2013, Steven Rostedt wrote:

quoted

 	c->tid = next_tid(c->tid);
-	c->page = NULL;
 	c->freelist = NULL;
+	c->page = NULL;

I'm assuming that this is to deal with the same CPU being able to touch
the code?

If so, it requires "barrier()". If this can affect other CPUs, then we
need a smp_wmb() here, and smp_rmb() where it matters.

This is dealing with the same cpu being interrupted. Some of these
segments are in interrupt disable sections so they are not affected.

The above is a section where interrupts are enabled so it needs the
barriers.

quoted

@@ -2227,8 +2227,8 @@ redo:
 	if (unlikely(!node_match(page, node))) {
 		stat(s, ALLOC_NODE_MISMATCH);
 		deactivate_slab(s, page, c->freelist);
-		c->page = NULL;
 		c->freelist = NULL;
+		c->page = NULL;
 		goto new_slab;
 	}

Interrupts are disabled so we do not need to change anything here.

quoted

@@ -2239,8 +2239,8 @@ redo:
 	 */
 	if (unlikely(!pfmemalloc_match(page, gfpflags))) {
 		deactivate_slab(s, page, c->freelist);
-		c->page = NULL;
 		c->freelist = NULL;
+		c->page = NULL;
 		goto new_slab;
 	}

Ditto which leaves us with:

Index: linux/mm/slub.c
===================================================================

--- linux.orig/mm/slub.c	2013-01-17 15:49:57.417491975 -0600
+++ linux/mm/slub.c	2013-01-17 15:50:49.010287150 -0600

@@ -1993,8 +1993,9 @@ static inline void flush_slab(struct kme
 	deactivate_slab(s, c->page, c->freelist);

 	c->tid = next_tid(c->tid);
-	c->page = NULL;
 	c->freelist = NULL;
+	barrier();
+	c->page = NULL;
 }

 /*

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