posix-cpu-timers: Do not arm SIGEV_NONE timers

There is no point in arming SIGEV_NONE timers as they never deliver a
signal. timer_gettime() is handling the expiry time correctly and that's
all SIGEV_NONE timers care about.

Prevent arming them and remove the expiry handler code which just disarms
them.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

kernel/time/posix-cpu-timers.c

@@ -584,12 +584,7 @@ static void cpu_timer_fire(struct k_itimer *timer)
 {
 	struct cpu_timer *ctmr = &timer->it.cpu;
 
-	if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
-		/*
-		 * User don't want any signal.
-		 */
-		cpu_timer_setexpires(ctmr, 0);
-	} else if (unlikely(timer->sigq == NULL)) {
+	if (unlikely(timer->sigq == NULL)) {
 		/*
 		 * This a special case for clock_nanosleep,
 		 * not a normal timer from sys_timer_create.
@@ -625,6 +620,7 @@ static void __posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *i
 static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 			       struct itimerspec64 *new, struct itimerspec64 *old)
 {
+	bool sigev_none = timer->it_sigev_notify == SIGEV_NONE;
 	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
 	u64 old_expires, new_expires, old_incr, val;
 	struct cpu_timer *ctmr = &timer->it.cpu;
@@ -688,7 +684,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 	if (CPUCLOCK_PERTHREAD(timer->it_clock))
 		val = cpu_clock_sample(clkid, p);
 	else
-		val = cpu_clock_sample_group(clkid, p, true);
+		val = cpu_clock_sample_group(clkid, p, !sigev_none);
 
 	/* Retrieve the previous expiry value if requested. */
 	if (old) {
@@ -708,19 +704,20 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 		goto out;
 	}
 
-	if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
+	/* Convert relative expiry time to absolute */
+	if (new_expires && !(timer_flags & TIMER_ABSTIME))
 		new_expires += val;
-	}
+
+	/* Set the new expiry time (might be 0) */
+	cpu_timer_setexpires(ctmr, new_expires);
 
 	/*
-	 * Install the new expiry time (or zero).
-	 * For a timer with no notification action, we don't actually
-	 * arm the timer (we'll just fake it for timer_gettime).
+	 * Arm the timer if it is not disabled, the new expiry value has
+	 * not yet expired and the timer requires signal delivery.
+	 * SIGEV_NONE timers are never armed.
 	 */
-	cpu_timer_setexpires(ctmr, new_expires);
-	if (new_expires != 0 && val < new_expires) {
+	if (!sigev_none && new_expires && val < new_expires)
 		arm_timer(timer, p);
-	}
 
 	unlock_task_sighand(p, &flags);
 	/*
@@ -739,7 +736,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 	timer->it_overrun_last = 0;
 	timer->it_overrun = -1;
 
-	if (val >= new_expires) {
+	if (!sigev_none && val >= new_expires) {
 		if (new_expires != 0) {
 			/*
 			 * The designated time already passed, so we notify