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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