linux-kernel - Re: [RFC PATCH v2] posix-timers: Support delivery of signals to the current thread

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Message-ID: <20230125124304.GA13746@redhat.com>
Date:   Wed, 25 Jan 2023 13:43:04 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marco Elver <elver@...gle.com>
Subject: Re: [RFC PATCH v2] posix-timers: Support delivery of signals to the
 current thread

On 01/12, Dmitry Vyukov wrote:
>
> --- a/kernel/time/posix-timers.c
> +++ b/kernel/time/posix-timers.c
> @@ -336,6 +336,7 @@ void posixtimer_rearm(struct kernel_siginfo *info)
>  int posix_timer_event(struct k_itimer *timr, int si_private)
>  {
>  	enum pid_type type;
> +	struct pid *pid;
>  	int ret;
>  	/*
>  	 * FIXME: if ->sigq is queued we can race with
> @@ -350,8 +351,9 @@ int posix_timer_event(struct k_itimer *timr, int si_private)
>  	 */
>  	timr->sigq->info.si_sys_private = si_private;
>
> +	pid = timr->it_pid ?: task_pid(current);
>  	type = !(timr->it_sigev_notify & SIGEV_THREAD_ID) ? PIDTYPE_TGID : PIDTYPE_PID;

can't resist... somehow the line above looks confusing to me, perhaps you
can change it to

	type = (timr->it_sigev_notify & SIGEV_THREAD_ID) ? PIDTYPE_PID : PIDTYPE_TGID;

> -static struct pid *good_sigevent(sigevent_t * event)
> +static struct pid *good_sigevent(sigevent_t *event, clockid_t which_clock)
>  {
>  	struct pid *pid = task_tgid(current);
>  	struct task_struct *rtn;
>
>  	switch (event->sigev_notify) {
>  	case SIGEV_SIGNAL | SIGEV_THREAD_ID:
> +		/* This will use the current task for signals. */
> +		if (which_clock == CLOCK_PROCESS_CPUTIME_ID &&
> +		    !event->sigev_notify_thread_id)
> +			return NULL;

this doesn't look right, this skips the "sigev_signo" check below.

Other than that I see nothing wrong in this patch, but I forgot everything
about posix timers many years ago ;)

> @@ -527,9 +534,11 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,
>
>  	if (event) {
>  		rcu_read_lock();
> -		new_timer->it_pid = get_pid(good_sigevent(event));
> +		pid = good_sigevent(event, which_clock);
> +		if (!IS_ERR(pid))
> +			new_timer->it_pid = get_pid(pid);

Another cosmetic nit, feel free to ignore... If you change good_sigevent()

	case SIGEV_NONE:
-		return pid;
+		return get_pid(pid);

you can remove this "if (!IS_ERR(pid))" code above.

Oleg.