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[202.181.97.72]) by mx.google.com with ESMTPS id w16si6084182otl.261.2019.01.29.02.34.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 29 Jan 2019 02:34:23 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of penguin-kernel@i-love.sakura.ne.jp designates 202.181.97.72 as permitted sender) client-ip=202.181.97.72; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of penguin-kernel@i-love.sakura.ne.jp designates 202.181.97.72 as permitted sender) smtp.mailfrom=penguin-kernel@i-love.sakura.ne.jp Received: from fsav304.sakura.ne.jp (fsav304.sakura.ne.jp [153.120.85.135]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x0TAY996049529; Tue, 29 Jan 2019 19:34:09 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav304.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav304.sakura.ne.jp); Tue, 29 Jan 2019 19:34:09 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav304.sakura.ne.jp) Received: from [192.168.1.8] (softbank126126163036.bbtec.net [126.126.163.36]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x0TAY4Pw049496 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Tue, 29 Jan 2019 19:34:09 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH v3] oom, oom_reaper: do not enqueue same task twice To: Johannes Weiner Cc: Michal Hocko , =?UTF-8?Q?Arkadiusz_Mi=c5=9bkiewicz?= , Andrew Morton , Tejun Heo , cgroups@vger.kernel.org, Aleksa Sarai , Jay Kamat , Roman Gushchin , linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm References: <6da6ca69-5a6e-a9f6-d091-f89a8488982a@gmail.com> <72aa8863-a534-b8df-6b9e-f69cf4dd5c4d@i-love.sakura.ne.jp> <33a07810-6dbc-36be-5bb6-a279773ccf69@i-love.sakura.ne.jp> <34e97b46-0792-cc66-e0f2-d72576cdec59@i-love.sakura.ne.jp> <2b0c7d6c-c58a-da7d-6f0a-4900694ec2d3@gmail.com> <1d161137-55a5-126f-b47e-b2625bd798ca@i-love.sakura.ne.jp> <20190127083724.GA18811@dhcp22.suse.cz> <20190127114021.GB18811@dhcp22.suse.cz> <20190128215315.GA2011@cmpxchg.org> From: Tetsuo Handa Message-ID: <5ee34fc6-1485-34f8-8790-903ddabaa809@i-love.sakura.ne.jp> Date: Tue, 29 Jan 2019 19:34:00 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190128215315.GA2011@cmpxchg.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Johannes Weiner wrote: > On Sun, Jan 27, 2019 at 11:57:38PM +0900, Tetsuo Handa wrote: > > This bug existed since the OOM reaper became invokable from > > task_will_free_mem(current) path in out_of_memory() in Linux 4.7, > > but memcg's group oom killing made it easier to trigger this bug by > > calling wake_oom_reaper() on the same task from one out_of_memory() > > request. > > This changelog seems a little terse compared to how tricky this is. > > Can you please include an explanation here *how* this bug is possible? > I.e. the race condition that causes the function te be entered twice > and the existing re-entrance check in there to fail. OK. Here is an updated patch. Only changelog part has changed. I hope this will provide enough information to stable kernel maintainers. ---------- From: Tetsuo Handa Subject: oom, oom_reaper: do not enqueue same task twice Arkadiusz reported that enabling memcg's group oom killing causes strange memcg statistics where there is no task in a memcg despite the number of tasks in that memcg is not 0. It turned out that there is a bug in wake_oom_reaper() which allows enqueuing same task twice which makes impossible to decrease the number of tasks in that memcg due to a refcount leak. This bug existed since the OOM reaper became invokable from task_will_free_mem(current) path in out_of_memory() in Linux 4.7, T1@P1 |T2@P1 |T3@P1 |OOM reaper ----------+----------+----------+------------ # Processing an OOM victim in a different memcg domain. try_charge() mem_cgroup_out_of_memory() mutex_lock(&oom_lock) 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() oom_kill_process(P1) do_send_sig_info(SIGKILL, @P1) mark_oom_victim(T1@P1) wake_oom_reaper(T1@P1) # T1@P1 is enqueued. mutex_unlock(&oom_lock) out_of_memory() mark_oom_victim(T2@P1) wake_oom_reaper(T2@P1) # T2@P1 is enqueued. mutex_unlock(&oom_lock) out_of_memory() mark_oom_victim(T1@P1) wake_oom_reaper(T1@P1) # T1@P1 is enqueued again due to oom_reaper_list == T2@P1 && T1@P1->oom_reaper_list == NULL. mutex_unlock(&oom_lock) # Completed processing an OOM victim in a different memcg domain. spin_lock(&oom_reaper_lock) # T1P1 is dequeued. spin_unlock(&oom_reaper_lock) but memcg's group oom killing made it easier to trigger this bug by calling wake_oom_reaper() on the same task from one out_of_memory() request. Fix this bug using an approach used by commit 855b018325737f76 ("oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task"). As a side effect of this patch, this patch also avoids enqueuing multiple threads sharing memory via task_will_free_mem(current) path. Fixes: af8e15cc85a25315 ("oom, oom_reaper: do not enqueue task if it is on the oom_reaper_list head") Signed-off-by: Tetsuo Handa Reported-by: Arkadiusz Miśkiewicz Tested-by: Arkadiusz Miśkiewicz Acked-by: Michal Hocko Acked-by: Roman Gushchin Cc: Tejun Heo Cc: Aleksa Sarai Cc: Jay Kamat Cc: Johannes Weiner --- include/linux/sched/coredump.h | 1 + mm/oom_kill.c | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index ec912d0..ecdc654 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -71,6 +71,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ +#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ diff --git a/mm/oom_kill.c b/mm/oom_kill.c index f0e8cd9..059e617 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -647,8 +647,8 @@ static int oom_reaper(void *unused) static void wake_oom_reaper(struct task_struct *tsk) { - /* tsk is already queued? */ - if (tsk == oom_reaper_list || tsk->oom_reaper_list) + /* mm is already queued? */ + if (test_and_set_bit(MMF_OOM_REAP_QUEUED, &tsk->signal->oom_mm->flags)) return; get_task_struct(tsk); -- 1.8.3.1