On Wed, Jul 30, 2014 at 03:41:54PM +0200, Frederic Weisbecker wrote:
> On Mon, Jul 28, 2014 at 03:56:12PM -0700, Paul E. McKenney wrote:
> > +/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
> > +static int __noreturn rcu_tasks_kthread(void *arg)
> > +{
> > + unsigned long flags;
> > + struct task_struct *g, *t;
> > + struct rcu_head *list;
> > + struct rcu_head *next;
> > +
> > + /* FIXME: Add housekeeping affinity. */
> > +
> > + /*
> > + * Each pass through the following loop makes one check for
> > + * newly arrived callbacks, and, if there are some, waits for
> > + * one RCU-tasks grace period and then invokes the callbacks.
> > + * This loop is terminated by the system going down. ;-)
> > + */
> > + for (;;) {
> > +
> > + /* Pick up any new callbacks. */
> > + raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
> > + smp_mb__after_unlock_lock(); /* Enforce GP memory ordering. */
> > + list = rcu_tasks_cbs_head;
> > + rcu_tasks_cbs_head = NULL;
> > + rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
> > + raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
> > +
> > + /* If there were none, wait a bit and start over. */
> > + if (!list) {
> > + schedule_timeout_interruptible(HZ);
> > + flush_signals(current);
> > + continue;
> > + }
> > +
> > + /*
> > + * There were callbacks, so we need to wait for an
> > + * RCU-tasks grace period. Start off by scanning
> > + * the task list for tasks that are not already
> > + * voluntarily blocked. Mark these tasks and make
> > + * a list of them in rcu_tasks_holdouts.
> > + */
> > + rcu_read_lock();
> > + do_each_thread(g, t) {
> > + if (t != current && ACCESS_ONCE(t->on_rq) &&
> > + !is_idle_task(t)) {
> > + t->rcu_tasks_holdout = 1;
> > + list_add(&t->rcu_tasks_holdout_list,
> > + &rcu_tasks_holdouts);
> > + }
> > + } while_each_thread(g, t);
> > + rcu_read_unlock();
>
> I think you need for_each_process_thread() to be RCU-safe.
> while_each_thread() has shown to be racy against exec even with
> rcu_read_lock().
Good catch, thank you!
Thanx, Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
