From: Oleg Nesterov <oleg@redhat.com> To: Mandeep Singh Baines <msb@chromium.org> Cc: Frederic Weisbecker <fweisbec@gmail.com>, Li Zefan <lizf@cn.fujitsu.com>, Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.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: Fri, 23 Mar 2012 18:51:57 +0100 [thread overview] Message-ID: <20120323175157.GA20675@redhat.com> (raw) In-Reply-To: <20120321185955.GK27051@google.com> On 03/21, Mandeep Singh Baines wrote: > > Oleg Nesterov (oleg@redhat.com) wrote: > > +/* > > + * rcu-safe, but should start at ->group_leader. > > + * thread_group_leader(g) protects against the race with exec which > > + * removes the leader from list. > > + * smp_rmb() pairs with implicit mb() implied by unlock + lock in > > + * de_thread()->release_task() path. > > + */ > > +#define while_each_thread_rcu(g, t) \ > > + while ((t = next_thread(t)) != g && \ > > + ({ smp_rmb(); thread_group_leader(g); })) > > + > > Couldn't you miss the exec_thread if: > > t = exec_thread && !thread_group_leader(g) Yes, we already discussed this, iirc. I was going to write that this is fine, but then I changed my mind. Indeed, it is not good while_each_thread_rcu() can miss the new leader. > Could we change do_prlimit()? Especially since its slow path. But do_prlimit() is correct. It sees the unhashed task under tasklist, task->group_leader should be correct. > I really like you're earlier solution (ignoring barrier): > > #define while_each_thread(g, t) \ > while (t->group_leader == g->group_leader && (t = next_thread(t)) != g) The problem is "ignoring barrier and races". OK, I'll try to think again. Oleg.
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From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> To: Mandeep Singh Baines <msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> Cc: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@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: Fri, 23 Mar 2012 18:51:57 +0100 [thread overview] Message-ID: <20120323175157.GA20675@redhat.com> (raw) In-Reply-To: <20120321185955.GK27051-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> On 03/21, Mandeep Singh Baines wrote: > > Oleg Nesterov (oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org) wrote: > > +/* > > + * rcu-safe, but should start at ->group_leader. > > + * thread_group_leader(g) protects against the race with exec which > > + * removes the leader from list. > > + * smp_rmb() pairs with implicit mb() implied by unlock + lock in > > + * de_thread()->release_task() path. > > + */ > > +#define while_each_thread_rcu(g, t) \ > > + while ((t = next_thread(t)) != g && \ > > + ({ smp_rmb(); thread_group_leader(g); })) > > + > > Couldn't you miss the exec_thread if: > > t = exec_thread && !thread_group_leader(g) Yes, we already discussed this, iirc. I was going to write that this is fine, but then I changed my mind. Indeed, it is not good while_each_thread_rcu() can miss the new leader. > Could we change do_prlimit()? Especially since its slow path. But do_prlimit() is correct. It sees the unhashed task under tasklist, task->group_leader should be correct. > I really like you're earlier solution (ignoring barrier): > > #define while_each_thread(g, t) \ > while (t->group_leader == g->group_leader && (t = next_thread(t)) != g) The problem is "ignoring barrier and races". OK, I'll try to think again. Oleg.
next prev parent reply other threads:[~2012-03-23 17:59 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 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 [this message] 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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