[PATCH] mm/slub: disallow obj's allocation on page with mismatched pfmemalloc purpose

[Pingfan Liu <kernelfans@gmail.com>]

new_slab_objects() always return c->page matching the required gfpflags,
but the current code is misleading and ___slab_alloc->deactivate_slab seems
to allow not-pfmemalloc purpose obj to be allocated from pfmemalloc-purpose
page. This patch re-organize the code to eliminate the confusion.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/slub.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index a68c2ae..e152634 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2551,23 +2551,21 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	}
 
 	freelist = new_slab_objects(s, gfpflags, node, &c);
-
 	if (unlikely(!freelist)) {
 		slab_out_of_memory(s, gfpflags, node);
 		return NULL;
 	}
 
+	VM_BUG_ON(!pfmemalloc_match(page, gfpflags));
 	page = c->page;
-	if (likely(!kmem_cache_debug(s) && pfmemalloc_match(page, gfpflags)))
+	if (likely(!kmem_cache_debug(s))
 		goto load_freelist;
 
 	/* Only entered in the debug case */
-	if (kmem_cache_debug(s) &&
-			!alloc_debug_processing(s, page, freelist, addr))
+	if (!alloc_debug_processing(s, page, freelist, addr))
 		goto new_slab;	/* Slab failed checks. Next slab needed */
-
-	deactivate_slab(s, page, get_freepointer(s, freelist), c);
-	return freelist;
+	else
+		goto load_freelist;
 }
 
 /*
-- 
2.7.4