Re: bug in memcg oom-killer results in a hung syscall in another process in the same cgroup
From: Shayan Pooya <hidden>
Date: 2016-07-14 15:35:30
Also in:
linux-mm, lkml
Well, but we can't do this. And "as expected" is actually just wrong. I still think that the whole FAULT_FLAG_USER logic is not right. This needs another email.
I meant as expected from the content of the patch :) I think Konstantin agrees that this patch cannot be merged upstream.
fork() should not fail because there is a memory hog in the same memcg. Worse, pthread_create() can kill the caller by the same reason. And we have the same or even worse problem with ->clear_child_tid, pthread_join() can hang forever. Unlikely we want to kill the application in this case ;) And in fact I think that the problem has nothing to do with set/claer_child_tid in particular. I am just curious... can you reproduce the problem reliably? If yes, can you try the patch below ? Just in case, this is not the real fix in any case...
Yes. It deterministically results in hung processes in vanilla kernel. I'll try this patch.
quoted hunk ↗ jump to hunk
--- x/kernel/sched/core.c +++ x/kernel/sched/core.c@@ -2793,8 +2793,11 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev) balance_callback(rq); preempt_enable(); - if (current->set_child_tid) + if (current->set_child_tid) { + mem_cgroup_oom_enable(); put_user(task_pid_vnr(current), current->set_child_tid); + mem_cgroup_oom_disable(); + } } /*
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