From: Oleg Nesterov <oleg@redhat.com> To: David Rientjes <rientjes@google.com> Cc: Andrew Morton <akpm@linux-foundation.org>, anfei <anfei.zhou@gmail.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, nishimura@mxp.nes.nec.co.jp, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Mel Gorman <mel@csn.ul.ie>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom_adj Date: Thu, 1 Apr 2010 17:37:56 +0200 [thread overview] Message-ID: <20100401153756.GD14603@redhat.com> (raw) In-Reply-To: <alpine.DEB.2.00.1004010128050.6285@chino.kir.corp.google.com> On 04/01, David Rientjes wrote: > > On Thu, 1 Apr 2010, Oleg Nesterov wrote: > > > > That doesn't work for depraceted_mode (sic), you'd need to test for > > > OOM_ADJUST_MIN and OOM_ADJUST_MAX in that case. > > > > Yes, probably "if (depraceted_mode)" should do more checks, I didn't try > > to verify that MIN/MAX are correctly converted. I showed this code to explain > > what I mean. > > > > Ok, please cc me on the patch, it will be good to get rid of the duplicate > code and remove oom_adj from struct signal_struct. OK, great, will do tomorrow. > Do we need ->siglock? Why can't we just do > > struct sighand_struct *sighand; > struct signal_struct *sig; > > rcu_read_lock(); > sighand = rcu_dereference(task->sighand); > if (!sighand) { > rcu_read_unlock(); > return; > } > sig = task->signal; > > ... load/store to sig ... > > rcu_read_unlock(); No. Before signals-make-task_struct-signal-immutable-refcountable.patch (actually, series of patches), this can't work. ->signal is not protected by rcu, and ->sighand != NULL doesn't mean ->signal != NULL. (yes, thread_group_cputime() is wrong too, but currently it is never called lockless). After signals-make-task_struct-signal-immutable-refcountable.patch, we do not need any checks at all, it is always safe to use ->signal. But. Unless we kill signal->oom_adj, we have another reason for ->siglock, we can't update both oom_adj and oom_score_adj atomically, and if we race with another thread they can be inconsistent wrt each other. Yes, oom_adj is not actually used, except we report it back to user-space, but still. So, I am going to send 2 patches. The first one factors out the code in base.c and kills signal->oom_adj, the next one removes ->siglock. Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com> To: David Rientjes <rientjes@google.com> Cc: Andrew Morton <akpm@linux-foundation.org>, anfei <anfei.zhou@gmail.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, nishimura@mxp.nes.nec.co.jp, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Mel Gorman <mel@csn.ul.ie>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom_adj Date: Thu, 1 Apr 2010 17:37:56 +0200 [thread overview] Message-ID: <20100401153756.GD14603@redhat.com> (raw) In-Reply-To: <alpine.DEB.2.00.1004010128050.6285@chino.kir.corp.google.com> On 04/01, David Rientjes wrote: > > On Thu, 1 Apr 2010, Oleg Nesterov wrote: > > > > That doesn't work for depraceted_mode (sic), you'd need to test for > > > OOM_ADJUST_MIN and OOM_ADJUST_MAX in that case. > > > > Yes, probably "if (depraceted_mode)" should do more checks, I didn't try > > to verify that MIN/MAX are correctly converted. I showed this code to explain > > what I mean. > > > > Ok, please cc me on the patch, it will be good to get rid of the duplicate > code and remove oom_adj from struct signal_struct. OK, great, will do tomorrow. > Do we need ->siglock? Why can't we just do > > struct sighand_struct *sighand; > struct signal_struct *sig; > > rcu_read_lock(); > sighand = rcu_dereference(task->sighand); > if (!sighand) { > rcu_read_unlock(); > return; > } > sig = task->signal; > > ... load/store to sig ... > > rcu_read_unlock(); No. Before signals-make-task_struct-signal-immutable-refcountable.patch (actually, series of patches), this can't work. ->signal is not protected by rcu, and ->sighand != NULL doesn't mean ->signal != NULL. (yes, thread_group_cputime() is wrong too, but currently it is never called lockless). After signals-make-task_struct-signal-immutable-refcountable.patch, we do not need any checks at all, it is always safe to use ->signal. But. Unless we kill signal->oom_adj, we have another reason for ->siglock, we can't update both oom_adj and oom_score_adj atomically, and if we race with another thread they can be inconsistent wrt each other. Yes, oom_adj is not actually used, except we report it back to user-space, but still. So, I am going to send 2 patches. The first one factors out the code in base.c and kills signal->oom_adj, the next one removes ->siglock. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2010-04-01 17:02 UTC|newest] Thread overview: 197+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-03-24 16:25 [PATCH] oom killer: break from infinite loop Anfei Zhou 2010-03-24 16:25 ` Anfei Zhou 2010-03-25 2:51 ` KOSAKI Motohiro 2010-03-25 2:51 ` KOSAKI Motohiro 2010-03-26 22:08 ` Andrew Morton 2010-03-26 22:08 ` Andrew Morton 2010-03-26 22:33 ` Oleg Nesterov 2010-03-26 22:33 ` Oleg Nesterov 2010-03-28 14:55 ` anfei 2010-03-28 14:55 ` anfei 2010-03-28 16:28 ` Oleg Nesterov 2010-03-28 16:28 ` Oleg Nesterov 2010-03-28 21:21 ` David Rientjes 2010-03-28 21:21 ` David Rientjes 2010-03-29 11:21 ` Oleg Nesterov 2010-03-29 11:21 ` Oleg Nesterov 2010-03-29 20:49 ` [patch] oom: give current access to memory reserves if it has been killed David Rientjes 2010-03-29 20:49 ` David Rientjes 2010-03-30 15:46 ` Oleg Nesterov 2010-03-30 15:46 ` Oleg Nesterov 2010-03-30 20:26 ` David Rientjes 2010-03-30 20:26 ` David Rientjes 2010-03-31 17:58 ` Oleg Nesterov 2010-03-31 17:58 ` Oleg Nesterov 2010-03-31 20:47 ` Oleg Nesterov 2010-03-31 20:47 ` Oleg Nesterov 2010-04-01 8:35 ` David Rientjes 2010-04-01 8:35 ` David Rientjes 2010-04-01 8:57 ` [patch -mm] oom: hold tasklist_lock when dumping tasks David Rientjes 2010-04-01 14:27 ` Oleg Nesterov 2010-04-01 19:16 ` David Rientjes 2010-04-01 13:59 ` [patch] oom: give current access to memory reserves if it has been killed Oleg Nesterov 2010-04-01 14:00 ` Oleg Nesterov 2010-04-01 19:12 ` David Rientjes 2010-04-01 19:12 ` David Rientjes 2010-04-02 11:14 ` Oleg Nesterov 2010-04-02 11:14 ` Oleg Nesterov 2010-04-02 18:30 ` [PATCH -mm 0/4] oom: linux has threads Oleg Nesterov 2010-04-02 18:30 ` Oleg Nesterov 2010-04-02 18:31 ` [PATCH -mm 1/4] oom: select_bad_process: check PF_KTHREAD instead of !mm to skip kthreads Oleg Nesterov 2010-04-02 18:31 ` Oleg Nesterov 2010-04-02 19:05 ` David Rientjes 2010-04-02 19:05 ` David Rientjes 2010-04-02 18:32 ` [PATCH -mm 2/4] oom: select_bad_process: PF_EXITING check should take ->mm into account Oleg Nesterov 2010-04-02 18:32 ` Oleg Nesterov 2010-04-06 11:42 ` anfei 2010-04-06 11:42 ` anfei 2010-04-06 12:18 ` Oleg Nesterov 2010-04-06 12:18 ` Oleg Nesterov 2010-04-06 13:05 ` anfei 2010-04-06 13:05 ` anfei 2010-04-06 13:38 ` Oleg Nesterov 2010-04-06 13:38 ` Oleg Nesterov 2010-04-02 18:32 ` [PATCH -mm 3/4] oom: introduce find_lock_task_mm() to fix !mm false positives Oleg Nesterov 2010-04-02 18:32 ` Oleg Nesterov 2010-04-02 18:33 ` [PATCH -mm 4/4] oom: oom_forkbomb_penalty: move thread_group_cputime() out of task_lock() Oleg Nesterov 2010-04-02 18:33 ` Oleg Nesterov 2010-04-02 19:04 ` David Rientjes 2010-04-02 19:04 ` David Rientjes 2010-04-05 14:23 ` [PATCH -mm] oom: select_bad_process: never choose tasks with badness == 0 Oleg Nesterov 2010-04-05 14:23 ` Oleg Nesterov 2010-04-02 19:02 ` [patch] oom: give current access to memory reserves if it has been killed David Rientjes 2010-04-02 19:02 ` David Rientjes 2010-04-02 19:14 ` Oleg Nesterov 2010-04-02 19:14 ` Oleg Nesterov 2010-04-02 19:46 ` David Rientjes 2010-04-02 19:46 ` David Rientjes 2010-04-02 19:54 ` [patch -mm] oom: exclude tasks with badness score of 0 from being selected David Rientjes 2010-04-02 19:54 ` David Rientjes 2010-04-02 21:04 ` Oleg Nesterov 2010-04-02 21:04 ` Oleg Nesterov 2010-04-02 21:22 ` [patch -mm v2] " David Rientjes 2010-04-02 21:22 ` David Rientjes 2010-04-02 20:55 ` [patch] oom: give current access to memory reserves if it has been killed Oleg Nesterov 2010-04-02 20:55 ` Oleg Nesterov 2010-03-31 21:07 ` David Rientjes 2010-03-31 21:07 ` David Rientjes 2010-03-31 22:50 ` Oleg Nesterov 2010-03-31 22:50 ` Oleg Nesterov 2010-03-31 23:30 ` Oleg Nesterov 2010-03-31 23:30 ` Oleg Nesterov 2010-03-31 23:48 ` David Rientjes 2010-03-31 23:48 ` David Rientjes 2010-04-01 14:39 ` Oleg Nesterov 2010-04-01 14:39 ` Oleg Nesterov 2010-04-01 18:58 ` David Rientjes 2010-04-01 18:58 ` David Rientjes 2010-04-01 8:25 ` David Rientjes 2010-04-01 8:25 ` David Rientjes 2010-04-01 15:26 ` Oleg Nesterov 2010-04-01 15:26 ` Oleg Nesterov 2010-04-08 21:08 ` David Rientjes 2010-04-08 21:08 ` David Rientjes 2010-04-09 12:38 ` Oleg Nesterov 2010-04-09 12:38 ` Oleg Nesterov 2010-03-30 16:39 ` [PATCH] oom: fix the unsafe proc_oom_score()->badness() call Oleg Nesterov 2010-03-30 16:39 ` Oleg Nesterov 2010-03-30 17:43 ` [PATCH -mm] proc: don't take ->siglock for /proc/pid/oom_adj Oleg Nesterov 2010-03-30 17:43 ` Oleg Nesterov 2010-03-30 20:30 ` David Rientjes 2010-03-30 20:30 ` David Rientjes 2010-03-31 9:17 ` Oleg Nesterov 2010-03-31 9:17 ` Oleg Nesterov 2010-03-31 18:59 ` Oleg Nesterov 2010-03-31 18:59 ` Oleg Nesterov 2010-03-31 21:14 ` David Rientjes 2010-03-31 21:14 ` David Rientjes 2010-03-31 23:00 ` Oleg Nesterov 2010-03-31 23:00 ` Oleg Nesterov 2010-04-01 8:32 ` David Rientjes 2010-04-01 8:32 ` David Rientjes 2010-04-01 15:37 ` Oleg Nesterov [this message] 2010-04-01 15:37 ` Oleg Nesterov 2010-04-01 19:04 ` David Rientjes 2010-04-01 19:04 ` David Rientjes 2010-03-30 20:32 ` [PATCH] oom: fix the unsafe proc_oom_score()->badness() call David Rientjes 2010-03-30 20:32 ` David Rientjes 2010-03-31 9:16 ` Oleg Nesterov 2010-03-31 9:16 ` Oleg Nesterov 2010-03-31 20:17 ` Oleg Nesterov 2010-03-31 20:17 ` Oleg Nesterov 2010-04-01 7:41 ` David Rientjes 2010-04-01 7:41 ` David Rientjes 2010-04-01 13:13 ` [PATCH 0/1] oom: fix the unsafe usage of badness() in proc_oom_score() Oleg Nesterov 2010-04-01 13:13 ` Oleg Nesterov 2010-04-01 13:13 ` [PATCH 1/1] " Oleg Nesterov 2010-04-01 13:13 ` Oleg Nesterov 2010-04-01 19:03 ` David Rientjes 2010-04-01 19:03 ` David Rientjes 2010-03-29 14:06 ` [PATCH] oom killer: break from infinite loop anfei 2010-03-29 14:06 ` anfei 2010-03-29 20:01 ` David Rientjes 2010-03-29 20:01 ` David Rientjes 2010-03-30 14:29 ` anfei 2010-03-30 14:29 ` anfei 2010-03-30 20:29 ` David Rientjes 2010-03-30 20:29 ` David Rientjes 2010-03-31 0:57 ` KAMEZAWA Hiroyuki 2010-03-31 0:57 ` KAMEZAWA Hiroyuki 2010-03-31 6:07 ` David Rientjes 2010-03-31 6:07 ` David Rientjes 2010-03-31 6:13 ` KAMEZAWA Hiroyuki 2010-03-31 6:13 ` KAMEZAWA Hiroyuki 2010-03-31 6:30 ` Balbir Singh 2010-03-31 6:30 ` Balbir Singh 2010-03-31 6:31 ` KAMEZAWA Hiroyuki 2010-03-31 6:31 ` KAMEZAWA Hiroyuki 2010-03-31 7:04 ` David Rientjes 2010-03-31 7:04 ` David Rientjes 2010-03-31 6:32 ` David Rientjes 2010-03-31 6:32 ` David Rientjes 2010-03-31 7:08 ` [patch -mm] memcg: make oom killer a no-op when no killable task can be found David Rientjes 2010-03-31 7:08 ` KAMEZAWA Hiroyuki 2010-03-31 8:04 ` Balbir Singh 2010-03-31 10:38 ` David Rientjes 2010-04-04 23:28 ` David Rientjes 2010-04-05 21:30 ` Andrew Morton 2010-04-05 22:40 ` David Rientjes 2010-04-05 22:49 ` Andrew Morton 2010-04-05 23:01 ` David Rientjes 2010-04-06 12:08 ` KOSAKI Motohiro 2010-04-06 21:47 ` David Rientjes 2010-04-07 0:20 ` KAMEZAWA Hiroyuki 2010-04-07 13:29 ` KOSAKI Motohiro 2010-04-08 18:05 ` David Rientjes 2010-04-21 19:17 ` Andrew Morton 2010-04-21 22:04 ` David Rientjes 2010-04-22 0:23 ` KAMEZAWA Hiroyuki 2010-04-22 8:34 ` David Rientjes 2010-04-27 22:58 ` [patch -mm] oom: reintroduce and deprecate oom_kill_allocating_task David Rientjes 2010-04-28 0:57 ` KAMEZAWA Hiroyuki 2010-04-22 7:23 ` [patch -mm] memcg: make oom killer a no-op when no killable task can be found Nick Piggin 2010-04-22 7:25 ` KAMEZAWA Hiroyuki 2010-04-22 10:09 ` Nick Piggin 2010-04-22 10:27 ` KAMEZAWA Hiroyuki 2010-04-22 21:11 ` David Rientjes 2010-04-22 10:28 ` David Rientjes 2010-04-22 15:39 ` Nick Piggin 2010-04-22 21:09 ` David Rientjes 2010-05-04 23:55 ` David Rientjes 2010-04-08 17:36 ` David Rientjes 2010-04-02 10:17 ` [PATCH] oom killer: break from infinite loop Mel Gorman 2010-04-02 10:17 ` Mel Gorman 2010-04-04 23:26 ` David Rientjes 2010-04-04 23:26 ` David Rientjes 2010-04-05 10:47 ` Mel Gorman 2010-04-05 10:47 ` Mel Gorman 2010-04-06 22:40 ` David Rientjes 2010-04-06 22:40 ` David Rientjes 2010-03-29 11:31 ` anfei 2010-03-29 11:31 ` anfei 2010-03-29 11:46 ` Oleg Nesterov 2010-03-29 11:46 ` Oleg Nesterov 2010-03-29 12:09 ` anfei 2010-03-29 12:09 ` anfei 2010-03-28 2:46 ` David Rientjes 2010-03-28 2:46 ` David Rientjes
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