From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 831C56B000C for ; Tue, 20 Mar 2018 08:52:30 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id i11so842095pgq.10 for ; Tue, 20 Mar 2018 05:52:30 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id i131si1137284pgc.347.2018.03.20.05.52.29 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Mar 2018 05:52:29 -0700 (PDT) Subject: Re: [PATCH 1/2] mm,oom_reaper: Show trace of unable to reap victim thread. From: Tetsuo Handa References: <1521547076-3399-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180320122818.GL23100@dhcp22.suse.cz> In-Reply-To: <20180320122818.GL23100@dhcp22.suse.cz> Message-Id: <201803202152.HED82804.QFOHLMVFFtOOJS@I-love.SAKURA.ne.jp> Date: Tue, 20 Mar 2018 21:52:33 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@suse.com Cc: linux-mm@kvack.org, rientjes@google.com Michal Hocko wrote: > On Tue 20-03-18 20:57:55, Tetsuo Handa wrote: > > I found that it is not difficult to hit "oom_reaper: unable to reap pid:" > > messages if the victim thread is doing copy_process(). Since I noticed > > that it is likely helpful to show trace of unable to reap victim thread > > for finding locations which should use killable wait, this patch does so. > > > > [ 226.608508] oom_reaper: unable to reap pid:9261 (a.out) > > [ 226.611971] a.out D13056 9261 6927 0x00100084 > > [ 226.615879] Call Trace: > > [ 226.617926] ? __schedule+0x25f/0x780 > > [ 226.620559] schedule+0x2d/0x80 > > [ 226.623356] rwsem_down_write_failed+0x2bb/0x440 > > [ 226.626426] ? rwsem_down_write_failed+0x55/0x440 > > [ 226.629458] ? anon_vma_fork+0x124/0x150 > > [ 226.632679] call_rwsem_down_write_failed+0x13/0x20 > > [ 226.635884] down_write+0x49/0x60 > > [ 226.638867] ? copy_process.part.41+0x12f2/0x1fe0 > > [ 226.642042] copy_process.part.41+0x12f2/0x1fe0 /* i_mmap_lock_write() in dup_mmap() */ > > [ 226.645087] ? _do_fork+0xe6/0x560 > > [ 226.647991] _do_fork+0xe6/0x560 > > [ 226.650495] ? syscall_trace_enter+0x1a9/0x240 > > [ 226.653443] ? retint_user+0x18/0x18 > > [ 226.656601] ? page_fault+0x2f/0x50 > > [ 226.659159] ? trace_hardirqs_on_caller+0x11f/0x1b0 > > [ 226.662399] do_syscall_64+0x74/0x230 > > [ 226.664989] entry_SYSCALL_64_after_hwframe+0x42/0xb7 > > A single stack trace in the changelog would be sufficient IMHO. > Appart from that. What do you expect users will do about this trace? > Sure they will see a path which holds mmap_sem, we will see a bug report > but we can hardly do anything about that. We simply cannot drop the lock > from that path in 99% of situations. So _why_ do we want to add more > information to the log? This case is blocked at i_mmap_lock_write(). If we can add error handling path there, we can replace i_mmap_lock_write() with i_mmap_lock_write_killable() and bail out soon. This patch helps finding such locations.