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[202.181.97.72]) by mx.google.com with ESMTPS id u4si3385701oig.17.2019.06.15.14.34.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 15 Jun 2019 14:34:38 -0700 (PDT) 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 fsav405.sakura.ne.jp (fsav405.sakura.ne.jp [133.242.250.104]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x5FLXux2063615; Sun, 16 Jun 2019 06:33:56 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav405.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav405.sakura.ne.jp); Sun, 16 Jun 2019 06:33:56 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav405.sakura.ne.jp) Received: from [192.168.1.8] (softbank126012062002.bbtec.net [126.12.62.2]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x5FLXpms063601 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Sun, 16 Jun 2019 06:33:56 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: general protection fault in oom_unkillable_task To: Shakeel Butt Cc: Michal Hocko , syzbot , Andrew Morton , "Eric W. Biederman" , Roman Gushchin , Johannes Weiner , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , LKML , Linux MM , syzkaller-bugs , yuzhoujian@didichuxing.com References: <0000000000004143a5058b526503@google.com> <20190615134955.GA28441@dhcp22.suse.cz> <5bb1fe5d-f0e1-678b-4f64-82c8d5d81f61@i-love.sakura.ne.jp> From: Tetsuo Handa Message-ID: <791594c6-45a3-d78a-70b5-901aa580ed9f@i-love.sakura.ne.jp> Date: Sun, 16 Jun 2019 06:33:51 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: On 2019/06/16 3:50, Shakeel Butt wrote: >> While dump_tasks() traverses only each thread group, mem_cgroup_scan_tasks() >> traverses each thread. > > I think mem_cgroup_scan_tasks() traversing threads is not intentional > and css_task_iter_start in it should use CSS_TASK_ITER_PROCS as the > oom killer only cares about the processes or more specifically > mm_struct (though two different thread groups can have same mm_struct > but that is fine). We can't use CSS_TASK_ITER_PROCS from mem_cgroup_scan_tasks(). I've tried CSS_TASK_ITER_PROCS in an attempt to evaluate only one thread from each thread group, but I found that CSS_TASK_ITER_PROCS causes skipping whole threads in a thread group (and trivially allowing "Out of memory and no killable processes...\n" flood) if thread group leader has already exited. If we can agree with using a flag in mm_struct in order to track whether each mm_struct was already evaluated for each out_of_memory() call, we can printk() only one thread from all thread groups sharing that mm_struct...