From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io1-f70.google.com (mail-io1-f70.google.com [209.85.166.70]) by kanga.kvack.org (Postfix) with ESMTP id 3B8036B0280 for ; Wed, 17 Oct 2018 06:06:55 -0400 (EDT) Received: by mail-io1-f70.google.com with SMTP id c21-v6so24348554ioi.14 for ; Wed, 17 Oct 2018 03:06:55 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id c5-v6si12604709jae.126.2018.10.17.03.06.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Oct 2018 03:06:53 -0700 (PDT) From: Tetsuo Handa Subject: [PATCH v3] mm: memcontrol: Don't flood OOM messages with no eligible task. Date: Wed, 17 Oct 2018 19:06:22 +0900 Message-Id: <1539770782-3343-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Johannes Weiner , linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, guro@fb.com, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, rientjes@google.com, yang.s@alibaba-inc.com, Andrew Morton , Sergey Senozhatsky , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Tetsuo Handa , Michal Hocko , syzbot syzbot is hitting RCU stall at shmem_fault() [1]. This is because memcg-OOM events with no eligible task (current thread is marked as OOM-unkillable) continued calling dump_header() from out_of_memory() enabled by commit 3100dab2aa09dc6e ("mm: memcontrol: print proper OOM header when no eligible victim left."). Michal proposed ratelimiting dump_header() [2]. But I don't think that that patch is appropriate because that patch does not ratelimit "%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n" "Out of memory and no killable processes...\n" messages which can be printed for every few milliseconds (i.e. effectively denial of service for console users) until the OOM situation is solved. Let's make sure that next dump_header() waits for at least 60 seconds from previous "Out of memory and no killable processes..." message. Michal is thinking that any interval is meaningless without knowing the printk() throughput. But since printk() is synchronous unless handed over to somebody else by commit dbdda842fe96f893 ("printk: Add console owner and waiter logic to load balance console writes"), it is likely that all OOM messages from this out_of_memory() request is already flushed to consoles when pr_warn("Out of memory and no killable processes...\n") returned. Thus, we will be able to allow console users to do what they need to do. To summarize, this patch allows threads in requested memcg to complete memory allocation requests for doing recovery operation, and also allows administrators to manually do recovery operation from console if OOM-unkillable thread is failing to solve the OOM situation automatically. [1] https://syzkaller.appspot.com/bug?id=4ae3fff7fcf4c33a47c1192d2d62d2e03efffa64 [2] https://lkml.kernel.org/r/20181010151135.25766-1-mhocko@kernel.org Signed-off-by: Tetsuo Handa Reported-by: syzbot Cc: Johannes Weiner Cc: Michal Hocko --- mm/oom_kill.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f10aa53..9056f9b 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -1106,6 +1106,11 @@ bool out_of_memory(struct oom_control *oc) select_bad_process(oc); /* Found nothing?!?! */ if (!oc->chosen) { + static unsigned long last_warned; + + if ((is_sysrq_oom(oc) || is_memcg_oom(oc)) && + time_in_range(jiffies, last_warned, last_warned + 60 * HZ)) + return false; dump_header(oc, NULL); pr_warn("Out of memory and no killable processes...\n"); /* @@ -1115,6 +1120,7 @@ bool out_of_memory(struct oom_control *oc) */ if (!is_sysrq_oom(oc) && !is_memcg_oom(oc)) panic("System is deadlocked on memory\n"); + last_warned = jiffies; } if (oc->chosen && oc->chosen != (void *)-1UL) oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" : -- 1.8.3.1