Messages in this thread |  | | Date | Thu, 26 Apr 2018 18:18:20 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup |
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On 04/26, Peter Zijlstra wrote: > > For the others, I think we want to do something like the below. I still > need to look at TASK_TRACED, which I suspect is also special,
Yes, and TASK_STOPPED.
ptrace_freeze_traced() and ptrace_unfreeze_traced() should be fine, but ptrace_stop() wants set_special_state() too, I think.
> but ptrace always hurts my brain.
mine too ;)
> +/* > + * set_special_state() should be used for those states when the blocking task > + * can not use the regular condition based wait-loop. In that case we must > + * serialize against wakeups such that any possible in-flight TASK_RUNNING stores > + * will not collide with out state change. > + */ > +#define set_special_state(state_value) \ > + do { \ > + unsigned long flags; /* may shadow */ \ > + raw_spin_lock_irqsave(¤t->pi_lock, flags); \ > + current->state = (state_value); \ > + raw_spin_unlock_irqrestore(¤t->pi_lock, flags); \ > + } while (0) > +
Agreed.
I thought that perhaps we can change ttwu_do_wakeup() cmpxchg() instead of plain p->state = TASK_RUNNING, but this helper looks much more clear and simple.
Oleg.
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