It is possible that a single process group memcg easily swamps the log
with no-eligible OOM victim messages after current thread was OOM-killed,
due to race between the memcg charge and the OOM reaper [1].
Thread-1 Thread-2 OOM reaper
try_charge()
mem_cgroup_out_of_memory()
mutex_lock(oom_lock)
try_charge()
mem_cgroup_out_of_memory()
mutex_lock(oom_lock)
out_of_memory()
select_bad_process()
oom_kill_process(current)
wake_oom_reaper()
oom_reap_task()
# sets MMF_OOM_SKIP
mutex_unlock(oom_lock)
out_of_memory()
select_bad_process() # no task
mutex_unlock(oom_lock)
We don't need to invoke the memcg OOM killer if current thread was killed
when waiting for oom_lock, for mem_cgroup_oom_synchronize(true) and
memory_max_write() can bail out upon SIGKILL, and try_charge() allows
already killed/exiting threads to make forward progress.
Michal has a plan to use tsk_is_oom_victim() by calling mark_oom_victim()
on all thread groups sharing victim's mm. But fatal_signal_pending() in
this patch helps regardless of Michal's plan because it will avoid
needlessly calling out_of_memory() when current thread is already
terminating (e.g. got SIGINT after passing fatal_signal_pending() check
in try_charge() and mutex_lock_killable() did not block).
[1] https://lkml.kernel.org/r/ea637f9a-5dd0-f927-d26d-d0b4fd8ccb6f@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b860dd4f7..b0d3bf3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1389,8 +1389,13 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
};
bool ret;
- mutex_lock(&oom_lock);
- ret = out_of_memory(&oc);
+ if (mutex_lock_killable(&oom_lock))
+ return true;
+ /*
+ * A few threads which were not waiting at mutex_lock_killable() can
+ * fail to bail out. Therefore, check again after holding oom_lock.
+ */
+ ret = fatal_signal_pending(current) || out_of_memory(&oc);
mutex_unlock(&oom_lock);
return ret;
}
--
1.8.3.1
