Re: [PATCH] signal/posixtimers: Handle ignore/blocked sequences correctly

Frederic Weisbecker
2024-12-20T13:06:34Z

Le Thu, Dec 19, 2024 at 08:46:25PM +0100, Thomas Gleixner a écrit :
> kernel/signal.c | 38 +++++++++++++++++++++++++++++---------
> 1 file changed, 29 insertions(+), 9 deletions(-)
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2007,11 +2007,23 @@ void posixtimer_send_sigqueue(struct k_i
>
> if (!list_empty(&q->list)) {
> /*
> - * If task group is exiting with the signal already pending,
> - * wait for __exit_signal() to do its job. Otherwise if
> - * ignored, it's not supposed to be queued. Try to survive.
> + * The signal was ignored and blocked. The timer
> + * expiry queued it because blocked signals are
> + * queued independent of the ignored state.
> + *
> + * The unblocking set SIGPENDING, but the signal
> + * was not yet dequeued from the pending list,
> + * which would have put it back on the ignore list.

I must be missing something. I don't see dequeue_signal() checking if a signal
is ignored upon delivery.

> + * So prepare_signal() sees unblocked and ignored,
> + * which ends up here. Leave it queued like a
> + * regular signal.
> + *
> + * The same happens when the task group is exiting
> + * and the signal is already queued.
> + * prepare_signal() treats SIGNAL_GROUP_EXIT as
> + * ignored independent of its queued state. This
> + * gets cleaned up in __exit_signal().
> */
> - WARN_ON_ONCE(!(t->signal->flags & SIGNAL_GROUP_EXIT));
> goto out;
> }
>
> @@ -2046,17 +2058,25 @@ void posixtimer_send_sigqueue(struct k_i
> goto out;
> }
>
> - /* This should never happen and leaks a reference count */
> - if (WARN_ON_ONCE(!hlist_unhashed(&tmr->ignored_list)))
> - hlist_del_init(&tmr->ignored_list);
> -
> if (unlikely(!list_empty(&q->list))) {
> /* This holds a reference count already */
> result = TRACE_SIGNAL_ALREADY_PENDING;
> goto out;
> }
>
> - posixtimer_sigqueue_getref(q);
> + /*
> + * If the signal is on the ignore list, it got blocked after it was
> + * ignored earlier. But nothing lifted the ignore. Move it back to
> + * the pending list to be consistent with the regular signal
> + * handling. If it gets unblocked, it will be ignored again unless

I'm not sure about that. If I follow the sigprocmask() path, set_task_blocked()
doesn't take care about that. And later on, dequeue_signal() doesn't seem to
check either...

Thanks.

> + * a handler has been installed before unblocking. If it's not on
> + * the ignore list acquire a reference count.
> + */
> + if (likely(hlist_unhashed(&tmr->ignored_list)))
> + posixtimer_sigqueue_getref(q);
> + else
> + hlist_del_init(&tmr->ignored_list);
> +
> posixtimer_queue_sigqueue(q, t, tmr->it_pid_type);
> result = TRACE_SIGNAL_DELIVERED;