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SubjectRe: [PATCH 04/14] signal: don't notify parent if not stopping after tracehook_notify_jctl() in do_signal_stop()
On 11/26, Tejun Heo wrote:
>
> do_signal_stop() tests sig->group_stop_count one more time after
> calling tracehook_notify_jctl() as it's allowed release siglock. If
> group_stop_count has changed to zero, it no longer stops but still
> notifies the parent.

Only if tracehook_notify_jctl() returns nonzero. That was the
point, tracehook_ can ask to notify even if we are not going to
stop.

> Also, tracehook_notify_jctl() doesn't release siglock, so, currently,
> none of these matters at all.

Yes. But with this patch it is not possible to drop siglock in
tracehook_notify_jctl().

> This doesn't cause any behavior difference as the condition never
> triggers in the current code.

I don't understand the motivation then (probably I should read
the next patches).

If we kill the ability to drop ->siglock in tracehook_notify_jctl(),
we can simplify the code further. No need to start with
->group_stop_count = 1 and then decrement it again.

We could do something like

static int do_signal_stop(int signr)
{
struct signal_struct *sig = current->signal;
int notify;
if (sig->group_stop_count) {
--sig->group_stop_count;
} else {
struct task_struct *t;
if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
unlikely(signal_group_exit(sig)))
return 0;
/*
* There is no group stop already in progress.
* We must initiate one now.
*/
sig->group_exit_code = signr;
for (t = next_thread(current); t != current; t = next_thread(t))
/*
* Setting state to TASK_STOPPED for a group
* stop is always done with the siglock held,
* so this check has no races.
*/
if (!(t->flags & PF_EXITING) &&
!task_is_stopped_or_traced(t)) {
sig->group_stop_count++;
signal_wake_up(t, 0);
}
}
if (!sig->group_stop_count) {
sig->flags = SIGNAL_STOP_STOPPED;
current->exit_code = sig->group_exit_code;
__set_current_state(TASK_STOPPED);
notify = CLD_STOPPED;
}
spin_unlock_irq(&current->sighand->siglock);
if (notify || current->ptrace) {
read_lock(&tasklist_lock);
do_notify_parent_cldstop(current, notify);
read_unlock(&tasklist_lock);
}
/* Now we don't run again until woken by SIGCONT or SIGKILL */
schedule();
tracehook_finish_jctl();
current->exit_code = 0;

return 1;
}
In short, this patch dismisses tracehook_notify_jctl().

Roland?

Oleg.



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