From: Oleg Nesterov <oleg@redhat.com> To: Frederic Weisbecker <fweisbec@gmail.com> Cc: Li Zefan <lizf@cn.fujitsu.com>, Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Mandeep Singh Baines <msb@chromium.org>, Containers <containers@lists.linux-foundation.org>, Cgroups <cgroups@vger.kernel.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Paul Menage <paul@paulmenage.org>, Andrew Morton <akpm@linux-foundation.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking Date: Wed, 21 Dec 2011 14:08:48 +0100 [thread overview] Message-ID: <20111221130848.GA19679@redhat.com> (raw) In-Reply-To: <20111221034334.GD17668@somewhere> On 12/21, Frederic Weisbecker wrote: > Hi, > > Starring at some parts of cgroups, I have a few questions: > > - Is cgroup_enable_task_cg_list()'s while_each_thread() safe > against concurrent exec()? The leader may change in de_thread() > and invalidate the test done in while_each_thread(). Yes. Oh, we need to do something with while_each_thread. > - do_each_thread() also needs RCU and cgroup_enable_task_cg_list() > seems to remind it. But it seems there is at least one caller that > doesn't call rcu_read_lock(): update_cpu_mask() -> update_tasks_cpumask() -> cgroup_scan_tasks() I don't see any caller which takes rcu_read_lock... > - By the time we call cgroup_post_fork(), it is ready to be woken up > and usable by the scheduler. No, the new child can't run until do_fork()->wake_up_new_task(). > - Is the check for use_task_css_set_links in cgroup_post_fork() safe? given > it is checked outside css_set_lock? > > Imagine this: > > CPU 0 CPU 1 > ---- ----- > > cgroup_enable_task_cg() { > uset_tasks_css_set_links = 1 > for_each_thread() { > add tasks in the list > } > } > do_fork() { > cgroup_post_fork() { > use_tasks_css_set_links appears > to be equal to 0 due to write/read > not flushed. New task won't > appear to the list. Yes, I was thinking about this too. Or (I think) they can race "contrariwise". CPU_1 creates the new child, then CPU_0 sets uset_tasks_css_set_links = 1. But afaics there is no any guarantee that CPU_0 sees the result of list_add_tail_rcu(). Oleg.
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From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> To: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Cc: Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Mandeep Singh Baines <msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>, Paul Menage <paul-inf54ven1CmVyaH7bEyXVA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org> Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking Date: Wed, 21 Dec 2011 14:08:48 +0100 [thread overview] Message-ID: <20111221130848.GA19679@redhat.com> (raw) In-Reply-To: <20111221034334.GD17668@somewhere> On 12/21, Frederic Weisbecker wrote: > Hi, > > Starring at some parts of cgroups, I have a few questions: > > - Is cgroup_enable_task_cg_list()'s while_each_thread() safe > against concurrent exec()? The leader may change in de_thread() > and invalidate the test done in while_each_thread(). Yes. Oh, we need to do something with while_each_thread. > - do_each_thread() also needs RCU and cgroup_enable_task_cg_list() > seems to remind it. But it seems there is at least one caller that > doesn't call rcu_read_lock(): update_cpu_mask() -> update_tasks_cpumask() -> cgroup_scan_tasks() I don't see any caller which takes rcu_read_lock... > - By the time we call cgroup_post_fork(), it is ready to be woken up > and usable by the scheduler. No, the new child can't run until do_fork()->wake_up_new_task(). > - Is the check for use_task_css_set_links in cgroup_post_fork() safe? given > it is checked outside css_set_lock? > > Imagine this: > > CPU 0 CPU 1 > ---- ----- > > cgroup_enable_task_cg() { > uset_tasks_css_set_links = 1 > for_each_thread() { > add tasks in the list > } > } > do_fork() { > cgroup_post_fork() { > use_tasks_css_set_links appears > to be equal to 0 due to write/read > not flushed. New task won't > appear to the list. Yes, I was thinking about this too. Or (I think) they can race "contrariwise". CPU_1 creates the new child, then CPU_0 sets uset_tasks_css_set_links = 1. But afaics there is no any guarantee that CPU_0 sees the result of list_add_tail_rcu(). Oleg.
next prev parent reply other threads:[~2011-12-21 13:14 UTC|newest] Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-12-21 3:43 Q: cgroup: Questions about possible issues in cgroup locking Frederic Weisbecker 2011-12-21 3:43 ` Frederic Weisbecker 2011-12-21 13:08 ` Oleg Nesterov [this message] 2011-12-21 13:08 ` Oleg Nesterov 2011-12-21 17:56 ` Frederic Weisbecker 2011-12-21 17:56 ` Frederic Weisbecker 2011-12-21 19:01 ` Mandeep Singh Baines 2011-12-21 19:01 ` Mandeep Singh Baines [not found] ` <20111221190102.GE13529-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2011-12-21 19:08 ` Frederic Weisbecker 2011-12-21 19:08 ` Frederic Weisbecker 2011-12-21 19:24 ` Mandeep Singh Baines 2011-12-21 19:24 ` Mandeep Singh Baines [not found] ` <20111221192413.GF13529-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2011-12-21 20:04 ` Frederic Weisbecker 2011-12-21 20:04 ` Frederic Weisbecker 2011-12-21 20:04 ` Frederic Weisbecker 2011-12-22 15:30 ` Oleg Nesterov 2011-12-22 15:30 ` Oleg Nesterov [not found] ` <20111222153004.GA30522-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-04 19:36 ` Mandeep Singh Baines 2012-01-04 19:36 ` Mandeep Singh Baines 2012-01-04 19:36 ` Mandeep Singh Baines [not found] ` <20120104193614.GF9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-06 15:23 ` Oleg Nesterov 2012-01-06 15:23 ` Oleg Nesterov [not found] ` <20120106152356.GA23995-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-06 18:25 ` Mandeep Singh Baines 2012-01-06 18:25 ` Mandeep Singh Baines 2012-01-06 18:25 ` Mandeep Singh Baines [not found] ` <20120106182535.GJ9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-11 16:07 ` Oleg Nesterov 2012-01-11 16:07 ` Oleg Nesterov [not found] ` <20120111160730.GA24556-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-12 0:31 ` Mandeep Singh Baines 2012-01-12 0:31 ` Mandeep Singh Baines [not found] ` <20120112003102.GB9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-12 17:07 ` Oleg Nesterov 2012-01-12 17:07 ` Oleg Nesterov 2012-01-12 17:57 ` Mandeep Singh Baines 2012-01-12 17:57 ` Mandeep Singh Baines [not found] ` <20120112175725.GD9511-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-13 15:20 ` Oleg Nesterov 2012-01-13 15:20 ` Oleg Nesterov [not found] ` <20120113152010.GA19215-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-13 18:27 ` Mandeep Singh Baines 2012-01-13 18:27 ` Mandeep Singh Baines [not found] ` <20120113182750.GD18166-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-14 17:36 ` Oleg Nesterov 2012-01-14 17:36 ` Oleg Nesterov 2012-01-18 23:17 ` Mandeep Singh Baines 2012-01-18 23:17 ` Mandeep Singh Baines [not found] ` <20120118231742.GS18166-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-19 15:45 ` Oleg Nesterov 2012-01-19 15:45 ` Oleg Nesterov 2012-01-19 18:18 ` Mandeep Singh Baines 2012-01-19 18:18 ` Mandeep Singh Baines [not found] ` <20120119181803.GU18166-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-01-20 15:06 ` Oleg Nesterov 2012-01-20 15:06 ` Oleg Nesterov 2012-03-20 19:34 ` Oleg Nesterov 2012-03-20 19:34 ` Oleg Nesterov [not found] ` <20120320193414.GA21277-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-03-21 18:59 ` Mandeep Singh Baines 2012-03-21 18:59 ` Mandeep Singh Baines 2012-03-23 17:51 ` Oleg Nesterov 2012-03-23 17:51 ` Oleg Nesterov [not found] ` <20120321185955.GK27051-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> 2012-03-23 17:51 ` Oleg Nesterov [not found] ` <20120119154522.GA14058-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-19 18:18 ` Mandeep Singh Baines 2012-03-20 19:34 ` Oleg Nesterov [not found] ` <20120114173648.GA32543-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-18 23:17 ` Mandeep Singh Baines [not found] ` <20120112170728.GA25717-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2012-01-12 17:57 ` Mandeep Singh Baines 2011-12-22 15:30 ` Oleg Nesterov 2011-12-21 19:01 ` Mandeep Singh Baines 2012-02-01 16:28 ` Frederic Weisbecker 2012-02-01 16:28 ` Frederic Weisbecker [not found] ` <20111221130848.GA19679-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2011-12-21 17:56 ` Frederic Weisbecker 2011-12-21 17:59 ` Frederic Weisbecker 2011-12-21 17:59 ` Frederic Weisbecker 2011-12-21 18:11 ` Oleg Nesterov 2011-12-21 18:11 ` Oleg Nesterov [not found] ` <20111221181101.GA3092-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> 2011-12-21 18:23 ` Frederic Weisbecker 2011-12-21 18:23 ` Frederic Weisbecker 2011-12-21 18:23 ` Frederic Weisbecker 2012-02-01 16:28 ` Frederic Weisbecker 2011-12-21 13:08 ` Oleg Nesterov -- strict thread matches above, loose matches on Subject: below -- 2011-12-21 3:43 Frederic Weisbecker
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