mm: memcg: use proper memcg in limit bypass

Commit 84235de394d9 ("fs: buffer: move allocation failure loop into the
allocator") allowed __GFP_NOFAIL allocations to bypass the limit if they
fail to reclaim enough memory for the charge.  But because the main test
case was on a 3.2-based system, the patch missed the fact that on newer
kernels the charge function needs to return root_mem_cgroup when
bypassing the limit, and not NULL.  This will corrupt whatever memory is
at NULL + percpu pointer offset.  Fix this quickly before problems are
reported.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 497ec33ff22d..623d5c8bb1e1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2765,10 +2765,10 @@ done:
         *ptr = memcg;
         return 0;
 nomem:
-        *ptr = NULL;
-        if (gfp_mask & __GFP_NOFAIL)
-                return 0;
-        return -ENOMEM;
+        if (!(gfp_mask & __GFP_NOFAIL)) {
+                *ptr = NULL;
+                return -ENOMEM;
+        }
 bypass:
         *ptr = root_mem_cgroup;
         return -EINTR;