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SubjectRe: [PATCH 0.2/8] ptrace: Always put ptracee into appropriate execution state
On 03/22, Tejun Heo wrote:
>
> This patch updates __ptrace_unlink() such that GROUP_STOP_PENDING is
> reinstated regardless of the ptracee's current state as long as it's
> alive and makes sure that signal_wake_up() is called if execution
> state transition is necessary.

Looks correct (and the previous one too).

But I don't understand the PF_EXITING check,

> + /*
> + * Reinstate GROUP_STOP_PENDING if group stop is in effect and
> + * @child isn't dead.
> + */
> + if (!(child->flags & PF_EXITING) &&
> + (child->signal->flags & SIGNAL_STOP_STOPPED ||
> + child->signal->group_stop_count))
> + child->group_stop |= GROUP_STOP_PENDING;

Why do we need to filter out PF_EXITING tasks? This doesn't look
strictly necessary. And note that exit_signals() doesn't always
take ->siglock, we can race anyway.

> + * Note that @resume should be used iff @child
> + * is in TASK_TRACED; otherwise, we might unduly disrupt
> + * TASK_KILLABLE sleeps.

Yes. but, just in case,

> + */
> + if (child->group_stop & GROUP_STOP_PENDING || task_is_traced(child))
> + signal_wake_up(child, task_is_traced(child));

signal_wake_up() is not needed if task_is_traced(). Even if we added
GROUP_STOP_PENDING, ptrace_stop() does recalc_sigpending_tsk() anyway
before return.

So we could do

if (SIGNAL_STOP_STOPPED || group_stop_count) {
child->group_stop |= GROUP_STOP_PENDING;
signal_wake_up(child, 0);
}
if (task_is_traced(child))
wake_up_state(TASK_TRACED);
But probably a single wakeup looks more simple/clean, so I agree.

Oleg.



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