Messages in this thread | | | Date | Wed, 30 Jul 2014 09:10:35 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 1/9] rcu: Add call_rcu_tasks() |
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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
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