From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> To: Matt Helsley <matthltc-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org> Cc: rjw-KKrjLPT3xs0@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Subject: Re: [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking Date: Thu, 18 Oct 2012 15:35:17 -0700 [thread overview] Message-ID: <20121018223517.GQ13370@google.com> (raw) In-Reply-To: <20121018222155.GB6223-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> Hello, Matt. On Thu, Oct 18, 2012 at 03:21:55PM -0700, Matt Helsley wrote: > > Hmmm? Nothing prevents kthreads from being moved around. We only > > recently added the restriction to prevent migration of the kthreadd > > (the one which creates other kthreads). You can reproduce it with > > khungtask or any other !freezable kthreads. > > Ok. I don't immmediately see why that'd be a good idea but it's > possible.. Beats me too. There were talks about restricting all kthreads from being moved out of the root cgroup. Dunno. Maybe. > <off_topic> > "Whoever" did the freeze needs a way to "lock" access to the freezer state, > change the freezer state itself, do something (e.g. CRIU) which relies on > the state not changing, and then release the lock. Plus the lock has to be > released by the kernel if "Whoever" dies without the chance to release it. > So I was thinking who holds the lock and its lifetime could be represented > in userspace by file descriptor(s). > </off_topic> Long term, I don't think it's feasible to continue to use cgroup kernel interface as the multiplexing layer among different users. cgroup core simply doesn't have enough context or infrastructure to support such usages. It's somewhere between being a pure interface to the provided kernel feature and fully multiplexed interface which userland applications can depend on for arbitration. It tries to have the appearance of the latter but fails. I think the only sane way would be having a userland arbitrator which owns the kernel interface to itself and makes policy decisions from userland clients and configures cgroup accordingly. > > As for CRIU, it isn't using cgroup freezer at the moment because > > frozen tasks can't be ptraced currently. Something I'm hoping to > > change but not sure when it can be done. > > OK, but that doesn't mean the frozen nature of the task list itself > won't be useful in the future. I think that should be solved via userland policies rather than depending on this accidental cgroup_freezer feature. Thanks. -- tejun
WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj@kernel.org> To: Matt Helsley <matthltc@linux.vnet.ibm.com> Cc: rjw@sisk.pl, oleg@redhat.com, cgroups@vger.kernel.org, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHSET cgroup/for-3.8] cgroup_freezer: allow migration regardless of freezer state and update locking Date: Thu, 18 Oct 2012 15:35:17 -0700 [thread overview] Message-ID: <20121018223517.GQ13370@google.com> (raw) In-Reply-To: <20121018222155.GB6223@us.ibm.com> Hello, Matt. On Thu, Oct 18, 2012 at 03:21:55PM -0700, Matt Helsley wrote: > > Hmmm? Nothing prevents kthreads from being moved around. We only > > recently added the restriction to prevent migration of the kthreadd > > (the one which creates other kthreads). You can reproduce it with > > khungtask or any other !freezable kthreads. > > Ok. I don't immmediately see why that'd be a good idea but it's > possible.. Beats me too. There were talks about restricting all kthreads from being moved out of the root cgroup. Dunno. Maybe. > <off_topic> > "Whoever" did the freeze needs a way to "lock" access to the freezer state, > change the freezer state itself, do something (e.g. CRIU) which relies on > the state not changing, and then release the lock. Plus the lock has to be > released by the kernel if "Whoever" dies without the chance to release it. > So I was thinking who holds the lock and its lifetime could be represented > in userspace by file descriptor(s). > </off_topic> Long term, I don't think it's feasible to continue to use cgroup kernel interface as the multiplexing layer among different users. cgroup core simply doesn't have enough context or infrastructure to support such usages. It's somewhere between being a pure interface to the provided kernel feature and fully multiplexed interface which userland applications can depend on for arbitration. It tries to have the appearance of the latter but fails. I think the only sane way would be having a userland arbitrator which owns the kernel interface to itself and makes policy decisions from userland clients and configures cgroup accordingly. > > As for CRIU, it isn't using cgroup freezer at the moment because > > frozen tasks can't be ptraced currently. Something I'm hoping to > > change but not sure when it can be done. > > OK, but that doesn't mean the frozen nature of the task list itself > won't be useful in the future. I think that should be solved via userland policies rather than depending on this accidental cgroup_freezer feature. Thanks. -- tejun
next prev parent reply other threads:[~2012-10-18 22:35 UTC|newest] Thread overview: 149+ 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 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 [this message] 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 2012-10-16 22:28 Tejun Heo
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