slab: do ClearSlabPfmemalloc() for all pages of slab

Right now, we call ClearSlabPfmemalloc() for first page of slab when we
clear SlabPfmemalloc flag.  This is fine for most swap-over-network use
cases as it is expected that order-0 pages are in use.  Unfortunately it
is possible that that __ac_put_obj() checks SlabPfmemalloc on a tail
page and while this is harmless, it is sloppy.  This patch ensures that
the head page is always used.

This problem was originally identified by Joonsoo Kim.

[js1304@gmail.com: Original implementation and problem identification]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/slab.c b/mm/slab.c
index 811af03a14ef..d34a9034f929 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1000,7 +1000,7 @@ static void *__ac_get_obj(struct kmem_cache *cachep, struct array_cache *ac,
                 l3 = cachep->nodelists[numa_mem_id()];
                 if (!list_empty(&l3->slabs_free) && force_refill) {
                         struct slab *slabp = virt_to_slab(objp);
-                        ClearPageSlabPfmemalloc(virt_to_page(slabp->s_mem));
+                        ClearPageSlabPfmemalloc(virt_to_head_page(slabp->s_mem));
                         clear_obj_pfmemalloc(&objp);
                         recheck_pfmemalloc_active(cachep, ac);
                         return objp;
@@ -1032,7 +1032,7 @@ static void *__ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
 {
         if (unlikely(pfmemalloc_active)) {
                 /* Some pfmemalloc slabs exist, check if this is one */
-                struct page *page = virt_to_page(objp);
+                struct page *page = virt_to_head_page(objp);
                 if (PageSlabPfmemalloc(page))
                         set_obj_pfmemalloc(&objp);
         }