From: Oleg Nesterov <oleg@redhat.com> To: Tejun Heo <tj@kernel.org> Cc: rjw@sisk.pl, linux-kernel@vger.kernel.org, lizefan@huawei.com, containers@lists.linux-foundation.org, cgroups@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/1] freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() Date: Thu, 25 Oct 2012 19:34:33 +0200 [thread overview] Message-ID: <20121025173433.GA7650@redhat.com> (raw) In-Reply-To: <20121025171812.GE11442@htj.dyndns.org> On 10/25, Tejun Heo wrote: > > Hello, Oleg. > > On Thu, Oct 25, 2012 at 06:39:59PM +0200, Oleg Nesterov wrote: > > Change ptrace_stop() and do_signal_stop() to use freezable_schedule() > > rather than rely on subsequent try_to_freeze(). > > > > This allows to remove the task_is_stopped_or_traced() checks from > > try_to_freeze_tasks() and update_if_frozen(), and this fixes the > > unlikely race with ptrace_stop(). If the tracee does not schedule() > > it can miss a freezing condition. > > I think it would be great if the description is more detailed. This > code path always makes my head spin and I think we can definitely use > some more guiding in understanding this dang thing. :) Do you mean describe the race in more details? OK, will do and resend tomorrow. > > @@ -2092,7 +2085,7 @@ static bool do_signal_stop(int signr) > > } > > > > /* Now we don't run again until woken by SIGCONT or SIGKILL */ > > - schedule(); > > + freezable_schedule(); > > This makes me wonder whether we still need try_to_freeze() in > get_signal_to_deliver() right after the relock: label. Freezer no > longer treats STOPPED/TRACED special and both sleeping sites in signal > deliver path are marked freezable_schedule(). We shouldn't need the > explicit try_to_freeze(), right? OOPS. I'd say this doesn't really matter but yes we can move it up, get_signal_to_deliver() will be called again. But! the comment above try_to_freeze() becomes misleading with this patch, so this really needs v2. Thanks. Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Cc: rjw-KKrjLPT3xs0@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Subject: Re: [PATCH 1/1] freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() Date: Thu, 25 Oct 2012 19:34:33 +0200 [thread overview] Message-ID: <20121025173433.GA7650@redhat.com> (raw) In-Reply-To: <20121025171812.GE11442-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> On 10/25, Tejun Heo wrote: > > Hello, Oleg. > > On Thu, Oct 25, 2012 at 06:39:59PM +0200, Oleg Nesterov wrote: > > Change ptrace_stop() and do_signal_stop() to use freezable_schedule() > > rather than rely on subsequent try_to_freeze(). > > > > This allows to remove the task_is_stopped_or_traced() checks from > > try_to_freeze_tasks() and update_if_frozen(), and this fixes the > > unlikely race with ptrace_stop(). If the tracee does not schedule() > > it can miss a freezing condition. > > I think it would be great if the description is more detailed. This > code path always makes my head spin and I think we can definitely use > some more guiding in understanding this dang thing. :) Do you mean describe the race in more details? OK, will do and resend tomorrow. > > @@ -2092,7 +2085,7 @@ static bool do_signal_stop(int signr) > > } > > > > /* Now we don't run again until woken by SIGCONT or SIGKILL */ > > - schedule(); > > + freezable_schedule(); > > This makes me wonder whether we still need try_to_freeze() in > get_signal_to_deliver() right after the relock: label. Freezer no > longer treats STOPPED/TRACED special and both sleeping sites in signal > deliver path are marked freezable_schedule(). We shouldn't need the > explicit try_to_freeze(), right? OOPS. I'd say this doesn't really matter but yes we can move it up, get_signal_to_deliver() will be called again. But! the comment above try_to_freeze() becomes misleading with this patch, so this really needs v2. Thanks. Oleg.
next prev parent reply other threads:[~2012-10-25 17:33 UTC|newest] Thread overview: 148+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-10-16 22:28 [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking Tejun Heo 2012-10-16 22:28 ` Tejun Heo 2012-10-16 22:28 ` [PATCH 5/7] cgroup_freezer: allow moving tasks in and out of a frozen cgroup Tejun Heo [not found] ` <1350426526-14254-6-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2012-10-22 19:25 ` Oleg Nesterov 2012-10-22 19:25 ` Oleg Nesterov 2012-10-22 19:25 ` Oleg Nesterov 2012-10-22 21:25 ` Tejun Heo 2012-10-22 21:25 ` Tejun Heo 2012-10-23 16:14 ` Oleg Nesterov 2012-10-23 16:14 ` Oleg Nesterov [not found] ` <20121022212505.GG5951-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-23 16:14 ` Oleg Nesterov [not found] ` <20121022192506.GA27163-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-22 21:25 ` Tejun Heo 2012-10-19 16:54 ` [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking Rafael J. Wysocki 2012-10-19 16:54 ` Rafael J. Wysocki 2012-10-19 20:04 ` Tejun Heo 2012-10-19 20:04 ` Tejun Heo [not found] ` <20121019200421.GO13370-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-10-21 19:18 ` Oleg Nesterov 2012-10-21 19:18 ` Oleg Nesterov [not found] ` <20121021191853.GB26218-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-21 19:24 ` Tejun Heo 2012-10-21 19:24 ` Tejun Heo [not found] ` <2424755.Pg0O5tTD3k-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org> 2012-10-19 20:04 ` Tejun Heo [not found] ` <1350426526-14254-1-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2012-10-16 22:28 ` [PATCH 1/7] cgroup: cgroup_subsys->fork() should be called after the task is added to css_set Tejun Heo 2012-10-16 22:28 ` Tejun Heo [not found] ` <1350426526-14254-2-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2012-10-17 8:28 ` Li Zefan 2012-10-17 8:28 ` Li Zefan 2012-10-18 1:25 ` Li Zefan 2012-10-18 1:25 ` Li Zefan [not found] ` <507E6C4B.6000704-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> 2012-10-18 1:25 ` Li Zefan 2012-10-21 19:11 ` Oleg Nesterov 2012-10-21 19:11 ` Oleg Nesterov [not found] ` <20121021191141.GA26218-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-21 19:22 ` Tejun Heo 2012-10-21 19:22 ` Tejun Heo 2012-10-21 19:22 ` Tejun Heo [not found] ` <20121021192222.GB5951-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-22 18:04 ` Oleg Nesterov 2012-10-22 18:04 ` Oleg Nesterov [not found] ` <20121022180445.GB21553-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-22 21:16 ` Tejun Heo 2012-10-22 21:16 ` Tejun Heo [not found] ` <20121022211631.GE5951-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-23 15:51 ` Oleg Nesterov 2012-10-23 15:51 ` Oleg Nesterov [not found] ` <20121023155128.GB16201-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-24 19:04 ` Tejun Heo 2012-10-24 19:04 ` Tejun Heo [not found] ` <20121024190458.GB12182-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-25 17:42 ` Oleg Nesterov 2012-10-25 17:42 ` Oleg Nesterov 2012-12-20 5:25 ` Herton Ronaldo Krzesinski 2012-12-20 5:25 ` Herton Ronaldo Krzesinski 2012-12-28 21:22 ` [PATCH] cgroup: remove unused dummy cgroup_fork_callbacks() Tejun Heo 2012-12-28 21:22 ` Tejun Heo 2012-10-16 22:28 ` [PATCH 2/7] freezer: add missing mb's to freezer_count() and freezer_should_skip() Tejun Heo 2012-10-16 22:28 ` Tejun Heo [not found] ` <1350426526-14254-3-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2012-10-22 17:44 ` Oleg Nesterov 2012-10-22 17:44 ` Oleg Nesterov [not found] ` <20121022174404.GA21553-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-22 21:13 ` Tejun Heo 2012-10-22 21:13 ` Tejun Heo [not found] ` <20121022211317.GD5951-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-23 15:39 ` Oleg Nesterov 2012-10-23 15:39 ` Oleg Nesterov [not found] ` <20121023153919.GA16201-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-24 18:57 ` Tejun Heo 2012-10-24 18:57 ` Tejun Heo 2012-10-24 18:57 ` Tejun Heo [not found] ` <20121024185710.GA12182-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-25 16:39 ` [PATCH 0/1] (Was: freezer: add missing mb's to freezer_count() and freezer_should_skip()) Oleg Nesterov 2012-10-25 16:39 ` Oleg Nesterov [not found] ` <20121025163941.GA3801-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-25 16:39 ` [PATCH 1/1] freezer: change ptrace_stop/do_signal_stop to use freezable_schedule() Oleg Nesterov 2012-10-25 16:39 ` Oleg Nesterov 2012-10-25 17:18 ` Tejun Heo 2012-10-25 17:18 ` Tejun Heo 2012-10-25 17:34 ` Oleg Nesterov [this message] 2012-10-25 17:34 ` Oleg Nesterov [not found] ` <20121025173433.GA7650-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-25 17:36 ` Tejun Heo 2012-10-25 17:36 ` Tejun Heo [not found] ` <20121025173632.GI11442-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> 2012-10-26 17:45 ` [PATCH v2 0/1] " Oleg Nesterov 2012-10-26 17:45 ` Oleg Nesterov [not found] ` <20121026174545.GA21639-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-26 17:46 ` [PATCH v2 1/1] " Oleg Nesterov 2012-10-26 17:46 ` Oleg Nesterov [not found] ` <20121026174606.GB21639-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-26 17:52 ` Tejun Heo 2012-10-26 17:52 ` Tejun Heo 2012-10-26 18:01 ` Oleg Nesterov 2012-10-26 18:01 ` Oleg Nesterov 2012-10-26 21:14 ` Rafael J. Wysocki 2012-10-26 21:14 ` Rafael J. Wysocki [not found] ` <2566006.UzAQbpOjNQ-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org> 2012-10-26 21:29 ` Rafael J. Wysocki 2012-10-26 21:29 ` Rafael J. Wysocki 2012-10-26 21:29 ` Tejun Heo 2012-10-26 21:29 ` Tejun Heo [not found] ` <20121026212909.GW11442-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> 2012-10-28 0:16 ` Rafael J. Wysocki 2012-10-28 0:16 ` Rafael J. Wysocki 2012-10-28 0:16 ` Rafael J. Wysocki [not found] ` <2718983.vORnrfWdbE-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org> 2012-10-26 21:29 ` Tejun Heo [not found] ` <20121026180149.GA22421-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-26 21:14 ` Rafael J. Wysocki [not found] ` <20121026175258.GV11442-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> 2012-10-26 18:01 ` Oleg Nesterov 2012-10-27 22:22 ` Ben Hutchings 2012-10-27 22:22 ` Ben Hutchings 2012-10-27 22:22 ` Ben Hutchings [not found] ` <1351376558.21585.1.camel-nDn/Rdv9kqW9Jme8/bJn5UCKIB8iOfG2tUK59QYPAWc@public.gmane.org> 2012-10-28 13:45 ` Oleg Nesterov 2012-10-28 13:45 ` Oleg Nesterov [not found] ` <20121025171812.GE11442-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> 2012-10-25 17:34 ` [PATCH " Oleg Nesterov [not found] ` <20121025163959.GB3801-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-25 17:18 ` Tejun Heo 2012-10-16 22:28 ` [PATCH 3/7] cgroup_freezer: make it official that writes to freezer.state don't fail Tejun Heo 2012-10-16 22:28 ` Tejun Heo 2012-10-16 22:28 ` [PATCH 4/7] cgroup_freezer: don't stall transition to FROZEN for PF_NOFREEZE or PF_FREEZER_SKIP tasks Tejun Heo 2012-10-16 22:28 ` Tejun Heo 2012-10-22 18:34 ` Oleg Nesterov 2012-10-22 18:34 ` Oleg Nesterov [not found] ` <20121022183453.GA24687-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-22 21:18 ` Tejun Heo 2012-10-22 21:18 ` Tejun Heo 2012-10-23 15:55 ` Oleg Nesterov 2012-10-23 15:55 ` Oleg Nesterov [not found] ` <20121023155533.GC16201-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-24 19:06 ` Tejun Heo 2012-10-24 19:06 ` Tejun Heo [not found] ` <20121024190651.GC12182-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-25 17:12 ` [PATCH 0/1] (Was: cgroup_freezer: don't stall transition to FROZEN for PF_NOFREEZE or PF_FREEZER_SKIP tasks) Oleg Nesterov 2012-10-25 17:12 ` Oleg Nesterov [not found] ` <20121025171236.GA6776-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-25 17:12 ` [PATCH 1/1] freezer: exec should clear PF_NOFREEZE along with PF_KTHREAD Oleg Nesterov 2012-10-25 17:12 ` Oleg Nesterov 2012-10-25 17:20 ` Tejun Heo 2012-10-25 17:20 ` Tejun Heo [not found] ` <20121025172016.GF11442-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> 2012-10-25 17:37 ` Oleg Nesterov 2012-10-25 17:37 ` Oleg Nesterov [not found] ` <20121025173756.GB7650-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-25 17:37 ` Tejun Heo 2012-10-25 17:37 ` Tejun Heo 2012-10-25 20:13 ` Rafael J. Wysocki [not found] ` <CAOS58YPAVVr=itauGD9eTpfRLSBLuM8Bpyuq9AP73MDr8dPmiQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2012-10-25 20:13 ` Rafael J. Wysocki [not found] ` <20121025171256.GB6776-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-10-25 17:20 ` Tejun Heo [not found] ` <20121022211822.GF5951-OlzNCW9NnSVy/B6EtB590w@public.gmane.org> 2012-10-23 15:55 ` [PATCH 4/7] cgroup_freezer: don't stall transition to FROZEN for PF_NOFREEZE or PF_FREEZER_SKIP tasks Oleg Nesterov [not found] ` <1350426526-14254-5-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 2012-10-22 18:34 ` Oleg Nesterov 2012-10-16 22:28 ` [PATCH 5/7] cgroup_freezer: allow moving tasks in and out of a frozen cgroup Tejun Heo 2012-10-16 22:28 ` [PATCH 6/7] cgroup_freezer: prepare update_if_frozen() for locking change Tejun Heo 2012-10-16 22:28 ` Tejun Heo 2012-10-16 22:28 ` [PATCH 7/7] cgroup_freezer: don't use cgroup_lock_live_group() Tejun Heo 2012-10-16 22:28 ` Tejun Heo 2012-10-17 19:16 ` [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking Matt Helsley 2012-10-17 19:16 ` Matt Helsley [not found] ` <20121017191606.GA6223-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> 2012-10-18 21:14 ` Tejun Heo 2012-10-18 21:14 ` Tejun Heo 2012-10-18 21:14 ` Tejun Heo [not found] ` <20121018211434.GI13370-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-10-18 22:21 ` Matt Helsley 2012-10-18 22:21 ` Matt Helsley [not found] ` <20121018222155.GB6223-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> 2012-10-18 22:35 ` Tejun Heo 2012-10-18 22:35 ` Tejun Heo [not found] ` <20121018223517.GQ13370-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-10-18 23:47 ` Matt Helsley 2012-10-18 23:47 ` Matt Helsley 2012-10-19 0:01 ` Tejun Heo 2012-10-19 0:01 ` Tejun Heo 2012-10-19 1:29 ` Matt Helsley 2012-10-19 1:29 ` Matt Helsley 2012-10-19 20:02 ` Tejun Heo 2012-10-19 20:02 ` Tejun Heo [not found] ` <20121019012945.GD6223-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> 2012-10-19 20:02 ` Tejun Heo [not found] ` <20121019000153.GZ13370-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-10-19 1:29 ` Matt Helsley [not found] ` <20121018234726.GC6223-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> 2012-10-19 0:01 ` Tejun Heo 2012-10-19 16:54 ` Rafael J. Wysocki
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