On Wed, 2011-06-15 at 20:46 +0200, Oleg Nesterov wrote: > On 06/15, Greg Kurz wrote: > > > > @@ -176,6 +177,17 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, > > if (tracer) > > tpid = task_pid_nr_ns(tracer, ns); > > } > > + actpid = 0; > > + sighand = rcu_dereference(p->sighand); > > + if (sighand) { > > + struct pid_namespace *pid_ns; > > + unsigned long flags; > > + spin_lock_irqsave(&sighand->siglock, flags); > > Well. This is not exactly right. We have lock_task_sighand() for this. > I see... ->sighand could change so we need the for(;;) loop in __lock_task_sighand() to be sure we have the right pointer, correct ? By the way, if we use lock_task_sighand() we'll end up with nested rcu_read_lock(): it will work but I don't know how it may affect performance... > But. Why do you need ->siglock? Why rcu_read_lock() is not enough? > Because there's a race with __exit_signal()->__unhash_process()->detach_pid() that can break task_active_pid_ns() and rcu won't help here (unless *perhaps* by modifying __exit_signal() but I don't want to mess with such a critical path). > Hmm. You don't even need pid_ns afaics, you could simply look at > pid->numbers[pid->level]. > True but I will have the same problem: detach_pid() nullifies the pid. Thanks for your comments. -- Greg _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers