Messages in this thread Patch in this message | | | Subject | Re: [PATCH] sched: Fix race between task_group and sched_task_group | From | Kirill Tkhai <> | Date | Tue, 28 Oct 2014 08:24:34 +0300 |
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В Вт, 28/10/2014 в 00:04 +0100, Oleg Nesterov пишет: > On 10/27, Kirill Tkhai wrote: > > > > +static void cpu_cgroup_fork(struct task_struct *task) > > +{ > > + sched_move_task(task); > > +} > > + > > static int cpu_cgroup_can_attach(struct cgroup_subsys_state *css, > > struct cgroup_taskset *tset) > > { > > @@ -8205,6 +8210,7 @@ struct cgroup_subsys cpu_cgrp_subsys = { > > .css_free = cpu_cgroup_css_free, > > .css_online = cpu_cgroup_css_online, > > .css_offline = cpu_cgroup_css_offline, > > + .fork = cpu_cgroup_fork, > > Agreed, but it seems that sched_move_task() -> task_css_check() can > complain if CONFIG_PROVE_RCU...
Thanks, Oleg.
> > cpu_cgroup_exit() too calls sched_move_task() without any lock, but > there is the PF_EXITING check and init_css_set can't go away. > > perhaps sched_move_task() should just take rcu_read_lock() and use > task_css() ? This lockdep_is_held(siglock) looks ugly, and iiuc we > need it to shut up the warning if autogroup_move_group() is the caller.
Shouldn't we do that in separate patch? How about this?
[PATCH]sched: Remove lockdep check in sched_move_task()
sched_move_task() is the only interface to change sched_task_group: cpu_cgrp_subsys methods and autogroup_move_group() use it.
Everything is synchronized by task_rq_lock(), so cpu_cgroup_attach() is ordered with other users of sched_move_task(). This means we do no need RCU here: if we've dereferenced a tg here, the .attach method hasn't been called for it yet.
Thus, we should pass "true" to task_css_check() to silence lockdep warnings.
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com> Reported-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index dde8adb..d77e6ee 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7403,8 +7403,12 @@ void sched_move_task(struct task_struct *tsk) if (unlikely(running)) put_prev_task(rq, tsk); - tg = container_of(task_css_check(tsk, cpu_cgrp_id, - lockdep_is_held(&tsk->sighand->siglock)), + /* + * All callers are synchronized by task_rq_lock(); we do not use RCU + * which is pointless here. Thus, we pass "true" to task_css_check() + * to prevent lockdep warnings. + */ + tg = container_of(task_css_check(tsk, cpu_cgrp_id, true), struct task_group, css); tg = autogroup_task_group(tsk, tg); tsk->sched_task_group = tg;
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