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>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 497ec33..623d5c8 100644 (file)
--- 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;