[PATCH v4 1/2] memcg: Prevent memcg caches to be both OFF_SLAB & OBJFREELIST_SLAB

[Thomas Garnier]

From: Greg Thelen <gthelen@xxxxxxxxxx>

While testing OBJFREELIST_SLAB integration with pagealloc, we found a
bug where kmem_cache(sys) would be created with both CFLGS_OFF_SLAB &
CFLGS_OBJFREELIST_SLAB. When it happened, critical allocations needed
for loading drivers or creating new caches will fail.

The original kmem_cache is created early making OFF_SLAB not possible.
When kmem_cache(sys) is created, OFF_SLAB is possible and if pagealloc
is enabled it will try to enable it first under certain conditions.
Given kmem_cache(sys) reuses the original flag, you can have both flags
at the same time.

This fix discards allocator specific flags from memcg before calling
create_cache.

The bug exists since 4.6-rc1 and affects testing debug pagealloc
configurations.

Fixes: b03a017bebc4 ("mm/slab: introduce new slab management type, OBJFREELIST_SLAB")
Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
Tested-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
---
Based on next-20161027
---
 mm/slab_common.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 71f0b28..329b038 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -533,8 +533,8 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
 
 	s = create_cache(cache_name, root_cache->object_size,
 			 root_cache->size, root_cache->align,
-			 root_cache->flags, root_cache->ctor,
-			 memcg, root_cache);
+			 root_cache->flags & CACHE_CREATE_MASK,
+			 root_cache->ctor, memcg, root_cache);
 	/*
 	 * If we could not create a memcg cache, do not complain, because
 	 * that's not critical at all as we can always proceed with the root
-- 
2.8.0.rc3.226.g39d4020