Messages in this thread | | | Subject | Re: [RFC][PATCH 0/5] Signal scalability series | From | Matt Fleming <> | Date | Fri, 30 Sep 2011 21:00:23 +0100 |
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On Fri, 2011-09-30 at 18:52 +0200, Oleg Nesterov wrote: > And, this patch adds 4 new locks: > > sighand_struct->action_lock > > signal_struct->ctrl_lock > signal_struct->shared_siglock > > task_struct->siglock > > Nice ;) For what? This should be justified, imho.
Well, sighand->siglock is seriously overused. It protects so much and I think it's pretty confusing. It took me long enough to figure out how many locks were really needed. But that's beside the point, having a single lock doesn't scale at all, and that's what this series is about.
> Hmm. Just out of curiosity, I blindly applied the whole series and poke > the _random_ function to look at, dequeue_signal(). And it looks wrong. > > spin_lock_irqsave(¤t->signal->ctrl_lock, flags); > current->jobctl |= JOBCTL_STOP_DEQUEUED; > > This signal->ctrl_lock can't help. A sig_kernel_stop() should be > dequeued under the same lock, and we shouldn't release it unless we > set JOBCTL_STOP_DEQUEUED. Otherwise we race with SIGCONT.
Hmm.. is that really a problem? Does the dequeue and setting JOBCTL_STOP_DEQUEUED actually need to be atomic? Does it matter if we have SIGCONT on the signal queue when we set JOBCTL_STOP_DEQUEUED?
> May be do_signal_stop() does something special? At first flance it doesn't. > But wait, it does while_each_thread() under ->ctrl_lock, why this is safe?
Why is it not safe? What scenario are you thinking of where that isn't safe?
> May be I was just lucky ;)
I doubt luck has anything to do with it ;-)
Thanks for the review!
-- Matt Fleming, Intel Open Source Technology Center
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