From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
Cc: syzbot <syzbot+bab151e82a4e973fa325@syzkaller.appspotmail.com>,
cgroups@vger.kernel.org, dvyukov@google.com, hannes@cmpxchg.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
syzkaller-bugs@googlegroups.com, vdavydov.dev@gmail.com
Subject: Re: WARNING in try_charge
Date: Tue, 7 Aug 2018 06:50:09 +0900 [thread overview]
Message-ID: <9c03213f-c099-378b-e9fd-ed6f2a2afdc3@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20180806205519.GO10003@dhcp22.suse.cz>
On 2018/08/07 5:55, Michal Hocko wrote:
> On Tue 07-08-18 05:46:04, Tetsuo Handa wrote:
>> On 2018/08/07 5:34, Michal Hocko wrote:
>>> On Tue 07-08-18 05:26:23, Tetsuo Handa wrote:
>>>> On 2018/08/07 2:56, Michal Hocko wrote:
>>>>> So the oom victim indeed passed the above force path after the oom
>>>>> invocation. But later on hit the page fault path and that behaved
>>>>> differently and for some reason the force path hasn't triggered. I am
>>>>> wondering how could we hit the page fault path in the first place. The
>>>>> task is already killed! So what the hell is going on here.
>>>>>
>>>>> I must be missing something obvious here.
>>>>>
>>>> YOU ARE OBVIOUSLY MISSING MY MAIL!
>>>>
>>>> I already said this is "mm, oom: task_will_free_mem(current) should ignore MMF_OOM_SKIP for once."
>>>> problem which you are refusing at https://www.spinics.net/lists/linux-mm/msg133774.html .
>>>> And you again ignored my mail. Very sad...
>>>
>>> Your suggestion simply didn't make much sense. There is nothing like
>>> first check is different from the rest.
>>>
>>
>> I don't think your patch is appropriate. It avoids hitting WARN(1) but does not avoid
>> unnecessary killing of OOM victims.
>>
>> If you look at https://syzkaller.appspot.com/text?tag=CrashLog&x=15a1c770400000 , you will
>> notice that both 23766 and 23767 are killed due to task_will_free_mem(current) == false.
>> This is "unnecessary killing of additional processes".
>
> Have you noticed the mere detail that the memcg has to kill any task
> attempting the charge because the hard limit is 0? There is simply no
> other way around. You cannot charge. There is no unnecessary killing.
> Full stop. We do allow temporary breach of the hard limit just to let
> the task die and uncharge on the way out.
>
select_bad_process() is called just because
task_will_free_mem("already killed current thread which has not completed __mmput()") == false
is a bug. I'm saying that the OOM killer should not give up as soon as MMF_OOM_SKIP is set.
static bool oom_has_pending_victims(struct oom_control *oc)
{
struct task_struct *p, *tmp;
bool ret = false;
bool gaveup = false;
if (is_sysrq_oom(oc))
return false;
/*
* Wait for pending victims until __mmput() completes or stalled
* too long.
*/
list_for_each_entry_safe(p, tmp, &oom_victim_list, oom_victim_list) {
struct mm_struct *mm = p->signal->oom_mm;
if (oom_unkillable_task(p, oc->memcg, oc->nodemask))
continue;
ret = true;
+ /*
+ * Since memcg OOM allows forced charge, we can safely wait
+ * until __mmput() completes.
+ */
+ if (is_memcg_oom(oc))
+ return true;
#ifdef CONFIG_MMU
/*
* Since the OOM reaper exists, we can safely wait until
* MMF_OOM_SKIP is set.
*/
if (!test_bit(MMF_OOM_SKIP, &mm->flags)) {
if (!oom_reap_target) {
get_task_struct(p);
oom_reap_target = p;
trace_wake_reaper(p->pid);
wake_up(&oom_reaper_wait);
}
#endif
continue;
}
#endif
/* We can wait as long as OOM score is decreasing over time. */
if (!victim_mm_stalling(p, mm))
continue;
gaveup = true;
list_del(&p->oom_victim_list);
/* Drop a reference taken by mark_oom_victim(). */
put_task_struct(p);
}
if (gaveup)
debug_show_all_locks();
return ret;
}
next prev parent reply other threads:[~2018-08-06 21:50 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-04 13:33 WARNING in try_charge syzbot
2018-08-04 13:45 ` Tetsuo Handa
2018-08-05 11:33 ` Tetsuo Handa
2018-08-05 8:14 ` syzbot
2018-08-06 9:15 ` Michal Hocko
2018-08-06 9:30 ` Dmitry Vyukov
2018-08-06 9:48 ` Michal Hocko
2018-08-06 10:34 ` Dmitry Vyukov
2018-08-06 11:02 ` Michal Hocko
2018-08-06 11:57 ` Dmitry Vyukov
2018-08-06 14:21 ` Michal Hocko
2018-08-06 14:58 ` Dmitry Vyukov
2018-08-06 17:30 ` Michal Hocko
2018-08-06 17:53 ` Dmitry Vyukov
2018-08-06 15:07 ` Dmitry Vyukov
2018-08-06 15:31 ` Johannes Weiner
2018-08-06 10:39 ` Dmitry Vyukov
2018-08-06 10:47 ` Tetsuo Handa
2018-08-06 11:09 ` Michal Hocko
2018-08-06 11:27 ` syzbot
2018-08-06 11:32 ` Michal Hocko
2018-08-06 11:58 ` Dmitry Vyukov
2018-08-06 14:41 ` Tetsuo Handa
2018-08-06 14:58 ` Michal Hocko
2018-08-06 15:12 ` Tetsuo Handa
2018-08-06 14:54 ` David Howells
2018-08-06 15:04 ` Tetsuo Handa
2018-08-06 11:00 ` syzbot
2018-08-06 15:32 ` Tetsuo Handa
2018-08-06 15:42 ` syzbot
2018-08-06 16:02 ` Tetsuo Handa
2018-08-06 17:44 ` Michal Hocko
2018-08-06 17:49 ` Dmitry Vyukov
2018-08-06 17:56 ` Michal Hocko
2018-08-06 18:13 ` Michal Hocko
2018-08-06 18:23 ` syzbot
2018-08-06 18:55 ` Michal Hocko
2018-08-06 19:12 ` syzbot
2018-08-06 19:45 ` Michal Hocko
2018-08-06 19:46 ` Michal Hocko
2018-08-07 11:18 ` Dmitry Vyukov
2018-08-07 11:25 ` Michal Hocko
2018-08-06 18:39 ` Michal Hocko
2018-08-06 20:26 ` Tetsuo Handa
2018-08-06 20:34 ` Michal Hocko
2018-08-06 20:46 ` Tetsuo Handa
2018-08-06 20:55 ` Michal Hocko
2018-08-06 21:50 ` Tetsuo Handa [this message]
2018-08-07 10:19 ` Tetsuo Handa
2018-08-09 13:57 ` Tetsuo Handa
2018-08-09 15:07 ` Michal Hocko
2018-08-09 21:05 ` Tetsuo Handa
2018-08-09 15:34 ` Johannes Weiner
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