mm: memcg: do not allow task about to OOM kill to bypass the limit

Commit 4942642080ea ("mm: memcg: handle non-error OOM situations more
gracefully") allowed tasks that already entered a memcg OOM condition to
bypass the memcg limit on subsequent allocation attempts hoping this
would expedite finishing the page fault and executing the kill.

David Rientjes is worried that this breaks memcg isolation guarantees
and since there is no evidence that the bypass actually speeds up fault
processing just change it so that these subsequent charge attempts fail
outright.  The notable exception being __GFP_NOFAIL charges which are
required to bypass the limit regardless.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: David Rientjes <rientjes@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-bt: David Rientjes <rientjes@google.com>
Cc: <stable@kernel.org>
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 f6a63f5b3827e9feb1b5dc1aae8e7f1a84c96c56..bf5e8945714944f896e2dc79b33b75a491da4794 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2694,7 +2694,7 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
                goto bypass;
 
        if (unlikely(task_in_memcg_oom(current)))
-               goto bypass;
+               goto nomem;
 
        if (gfp_mask & __GFP_NOFAIL)
                oom = false;