mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook()

When I use kfree_rcu() to free a large memory allocated by kmalloc_node(),
the following dump occurs.

  BUG: kernel NULL pointer dereference, address: 0000000000000020
  [...]
  Oops: 0000 [#1] SMP
  [...]
  Workqueue: events kfree_rcu_work
  RIP: 0010:__obj_to_index include/linux/slub_def.h:182 [inline]
  RIP: 0010:obj_to_index include/linux/slub_def.h:191 [inline]
  RIP: 0010:memcg_slab_free_hook+0x120/0x260 mm/slab.h:363
  [...]
  Call Trace:
    kmem_cache_free_bulk+0x58/0x630 mm/slub.c:3293
    kfree_bulk include/linux/slab.h:413 [inline]
    kfree_rcu_work+0x1ab/0x200 kernel/rcu/tree.c:3300
    process_one_work+0x207/0x530 kernel/workqueue.c:2276
    worker_thread+0x320/0x610 kernel/workqueue.c:2422
    kthread+0x13d/0x160 kernel/kthread.c:313
    ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

When kmalloc_node() a large memory, page is allocated, not slab, so when
freeing memory via kfree_rcu(), this large memory should not be used by
memcg_slab_free_hook(), because memcg_slab_free_hook() is is used for
slab.

Using page_objcgs_check() instead of page_objcgs() in
memcg_slab_free_hook() to fix this bug.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 270c6a7 ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data")
Signed-off-by: Wang Hai <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Reviewed-by: Kefeng Wang <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Wang Hai

mm/slab.h

@@ -346,7 +346,7 @@ static inline void memcg_slab_free_hook(struct kmem_cache *s_orig,
 			continue;
 
 		page = virt_to_head_page(p[i]);
-		objcgs = page_objcgs(page);
+		objcgs = page_objcgs_check(page);
 		if (!objcgs)
 			continue;