Merge tag 'posix-timers-2024-07-29' of...

Merge tag 'posix-timers-2024-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/core

Pull updates for posix timers and related signal code from Frederic Weisbecker:

  * Prepare posix timers selftests for upcoming changes:

	- Check signal behaviour sanity against SIG_IGN

	- Check signal behaviour sanity against timer
	  reprogramm/deletion

	- Check SIGEV_NONE pending expiry read

	- Check interval timer read on a pending SIGNAL

	- Check correct overrun count after signal block/unblock

  * Various consolidations:

	- timer get/set

	- signal queue

  * Fixes:
	- Correctly read SIGEV_NONE timers

	- Forward expiry while reading expired interval timers
	  with pending signal

	- Don't arm SIGEV_NONE timers

  * Various cleanups all over the place

fs/proc/base.c

@@ -2456,13 +2456,13 @@ static void *timers_start(struct seq_file *m, loff_t *pos)
 	if (!tp->sighand)
 		return ERR_PTR(-ESRCH);
 
-	return seq_list_start(&tp->task->signal->posix_timers, *pos);
+	return seq_hlist_start(&tp->task->signal->posix_timers, *pos);
 }
 
 static void *timers_next(struct seq_file *m, void *v, loff_t *pos)
 {
 	struct timers_private *tp = m->private;
-	return seq_list_next(v, &tp->task->signal->posix_timers, pos);
+	return seq_hlist_next(v, &tp->task->signal->posix_timers, pos);
 }
 
 static void timers_stop(struct seq_file *m, void *v)
@@ -2491,7 +2491,7 @@ static int show_timer(struct seq_file *m, void *v)
 		[SIGEV_THREAD] = "thread",
 	};
 
-	timer = list_entry((struct list_head *)v, struct k_itimer, list);
+	timer = hlist_entry((struct hlist_node *)v, struct k_itimer, list);
 	notify = timer->it_sigev_notify;
 
 	seq_printf(m, "ID: %d\n", timer->it_id);

fs/signalfd.c

@@ -159,7 +159,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info
 	DECLARE_WAITQUEUE(wait, current);
 
 	spin_lock_irq(&current->sighand->siglock);
-	ret = dequeue_signal(current, &ctx->sigmask, info, &type);
+	ret = dequeue_signal(&ctx->sigmask, info, &type);
 	switch (ret) {
 	case 0:
 		if (!nonblock)
@@ -174,7 +174,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info
 	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
-		ret = dequeue_signal(current, &ctx->sigmask, info, &type);
+		ret = dequeue_signal(&ctx->sigmask, info, &type);
 		if (ret != 0)
 			break;
 		if (signal_pending(current)) {

include/linux/posix-timers.h

@@ -158,7 +158,7 @@ static inline void posix_cputimers_init_work(void) { }
  * @rcu:		RCU head for freeing the timer.
  */
 struct k_itimer {
-	struct list_head	list;
+	struct hlist_node	list;
 	struct hlist_node	t_hash;
 	spinlock_t		it_lock;
 	const struct k_clock	*kclock;

include/linux/sched/signal.h

@@ -137,7 +137,7 @@ struct signal_struct {
 
 	/* POSIX.1b Interval Timers */
 	unsigned int		next_posix_timer_id;
-	struct list_head	posix_timers;
+	struct hlist_head	posix_timers;
 
 	/* ITIMER_REAL timer for the process */
 	struct hrtimer real_timer;
@@ -276,8 +276,7 @@ static inline void signal_set_stop_flags(struct signal_struct *sig,
 extern void flush_signals(struct task_struct *);
 extern void ignore_signals(struct task_struct *);
 extern void flush_signal_handlers(struct task_struct *, int force_default);
-extern int dequeue_signal(struct task_struct *task, sigset_t *mask,
-			  kernel_siginfo_t *info, enum pid_type *type);
+extern int dequeue_signal(sigset_t *mask, kernel_siginfo_t *info, enum pid_type *type);
 
 static inline int kernel_dequeue_signal(void)
 {
@@ -287,7 +286,7 @@ static inline int kernel_dequeue_signal(void)
 	int ret;
 
 	spin_lock_irq(&task->sighand->siglock);
-	ret = dequeue_signal(task, &task->blocked, &__info, &__type);
+	ret = dequeue_signal(&task->blocked, &__info, &__type);
 	spin_unlock_irq(&task->sighand->siglock);
 
 	return ret;

init/init_task.c

@@ -29,7 +29,7 @@ static struct signal_struct init_signals = {
 	.cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex),
 	.exec_update_lock = __RWSEM_INITIALIZER(init_signals.exec_update_lock),
 #ifdef CONFIG_POSIX_TIMERS
-	.posix_timers = LIST_HEAD_INIT(init_signals.posix_timers),
+	.posix_timers	= HLIST_HEAD_INIT,
 	.cputimer	= {
 		.cputime_atomic	= INIT_CPUTIME_ATOMIC,
 	},

kernel/fork.c

@@ -1861,7 +1861,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 	prev_cputime_init(&sig->prev_cputime);
 
 #ifdef CONFIG_POSIX_TIMERS
-	INIT_LIST_HEAD(&sig->posix_timers);
+	INIT_HLIST_HEAD(&sig->posix_timers);
 	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	sig->real_timer.function = it_real_fn;
 #endif

kernel/signal.c

@@ -618,20 +618,18 @@ static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
 }
 
 /*
- * Dequeue a signal and return the element to the caller, which is
- * expected to free it.
- *
- * All callers have to hold the siglock.
+ * Try to dequeue a signal. If a deliverable signal is found fill in the
+ * caller provided siginfo and return the signal number. Otherwise return
+ * 0.
  */
-int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
-		   kernel_siginfo_t *info, enum pid_type *type)
+int dequeue_signal(sigset_t *mask, kernel_siginfo_t *info, enum pid_type *type)
 {
+	struct task_struct *tsk = current;
 	bool resched_timer = false;
 	int signr;
 
-	/* We only dequeue private signals from ourselves, we don't let
-	 * signalfd steal them
-	 */
+	lockdep_assert_held(&tsk->sighand->siglock);
+
 	*type = PIDTYPE_PID;
 	signr = __dequeue_signal(&tsk->pending, mask, info, &resched_timer);
 	if (!signr) {
@@ -1940,10 +1938,11 @@ struct sigqueue *sigqueue_alloc(void)
 
 void sigqueue_free(struct sigqueue *q)
 {
-	unsigned long flags;
 	spinlock_t *lock = &current->sighand->siglock;
+	unsigned long flags;
 
-	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
+	if (WARN_ON_ONCE(!(q->flags & SIGQUEUE_PREALLOC)))
+		return;
 	/*
 	 * We must hold ->siglock while testing q->list
 	 * to serialize with collect_signal() or with
@@ -1971,7 +1970,10 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
 	unsigned long flags;
 	int ret, result;
 
-	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
+	if (WARN_ON_ONCE(!(q->flags & SIGQUEUE_PREALLOC)))
+		return 0;
+	if (WARN_ON_ONCE(q->info.si_code != SI_TIMER))
+		return 0;
 
 	ret = -1;
 	rcu_read_lock();
@@ -2006,7 +2008,6 @@ int send_sigqueue(struct sigqueue *q, struct pid *pid, enum pid_type type)
 		 * If an SI_TIMER entry is already queue just increment
 		 * the overrun count.
 		 */
-		BUG_ON(q->info.si_code != SI_TIMER);
 		q->info.si_overrun++;
 		result = TRACE_SIGNAL_ALREADY_PENDING;
 		goto out;
@@ -2793,8 +2794,7 @@ bool get_signal(struct ksignal *ksig)
 		type = PIDTYPE_PID;
 		signr = dequeue_synchronous_signal(&ksig->info);
 		if (!signr)
-			signr = dequeue_signal(current, &current->blocked,
-					       &ksig->info, &type);
+			signr = dequeue_signal(&current->blocked, &ksig->info, &type);
 
 		if (!signr)
 			break; /* will return 0 */
@@ -3648,7 +3648,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info,
 	signotset(&mask);
 
 	spin_lock_irq(&tsk->sighand->siglock);
-	sig = dequeue_signal(tsk, &mask, info, &type);
+	sig = dequeue_signal(&mask, info, &type);
 	if (!sig && timeout) {
 		/*
 		 * None ready, temporarily unblock those we're interested
@@ -3667,7 +3667,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info,
 		spin_lock_irq(&tsk->sighand->siglock);
 		__set_task_blocked(tsk, &tsk->real_blocked);
 		sigemptyset(&tsk->real_blocked);
-		sig = dequeue_signal(tsk, &mask, info, &type);
+		sig = dequeue_signal(&mask, info, &type);
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);
 

kernel/time/alarmtimer.c

@@ -574,15 +574,10 @@ static enum alarmtimer_restart alarm_handle_timer(struct alarm *alarm,
 					    it.alarm.alarmtimer);
 	enum alarmtimer_restart result = ALARMTIMER_NORESTART;
 	unsigned long flags;
-	int si_private = 0;
 
 	spin_lock_irqsave(&ptr->it_lock, flags);
 
-	ptr->it_active = 0;
-	if (ptr->it_interval)
-		si_private = ++ptr->it_requeue_pending;
-
-	if (posix_timer_event(ptr, si_private) && ptr->it_interval) {
+	if (posix_timer_queue_signal(ptr) && ptr->it_interval) {
 		/*
 		 * Handle ignored signals and rearm the timer. This will go
 		 * away once we handle ignored signals proper. Ensure that

kernel/time/posix-cpu-timers.c

@@ -453,6 +453,7 @@ static void disarm_timer(struct k_itimer *timer, struct task_struct *p)
 	struct cpu_timer *ctmr = &timer->it.cpu;
 	struct posix_cputimer_base *base;
 
+	timer->it_active = 0;
 	if (!cpu_timer_dequeue(ctmr))
 		return;
 
@@ -559,6 +560,7 @@ static void arm_timer(struct k_itimer *timer, struct task_struct *p)
 	struct cpu_timer *ctmr = &timer->it.cpu;
 	u64 newexp = cpu_timer_getexpires(ctmr);
 
+	timer->it_active = 1;
 	if (!cpu_timer_enqueue(&base->tqhead, ctmr))
 		return;
 
@@ -584,12 +586,8 @@ 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)) {
+	timer->it_active = 0;
+	if (unlikely(timer->sigq == NULL)) {
 		/*
 		 * This a special case for clock_nanosleep,
 		 * not a normal timer from sys_timer_create.
@@ -600,9 +598,9 @@ static void cpu_timer_fire(struct k_itimer *timer)
 		/*
 		 * One-shot timer.  Clear it as soon as it's fired.
 		 */
-		posix_timer_event(timer, 0);
+		posix_timer_queue_signal(timer);
 		cpu_timer_setexpires(ctmr, 0);
-	} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
+	} else if (posix_timer_queue_signal(timer)) {
 		/*
 		 * The signal did not get queued because the signal
 		 * was ignored, so we won't get any callback to
@@ -614,6 +612,8 @@ static void cpu_timer_fire(struct k_itimer *timer)
 	}
 }
 
+static void __posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp, u64 now);
+
 /*
  * Guts of sys_timer_settime for CPU timers.
  * This is called with the timer locked and interrupts disabled.
@@ -623,9 +623,10 @@ static void cpu_timer_fire(struct k_itimer *timer)
 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;
+	u64 old_expires, new_expires, now;
 	struct sighand_struct *sighand;
 	struct task_struct *p;
 	unsigned long flags;
@@ -662,10 +663,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 		return -ESRCH;
 	}
 
-	/*
-	 * Disarm any old timer after extracting its expiry time.
-	 */
-	old_incr = timer->it_interval;
+	/* Retrieve the current expiry time before disarming the timer */
 	old_expires = cpu_timer_getexpires(ctmr);
 
 	if (unlikely(timer->it.cpu.firing)) {
@@ -673,157 +671,122 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
 		ret = TIMER_RETRY;
 	} else {
 		cpu_timer_dequeue(ctmr);
+		timer->it_active = 0;
 	}
 
 	/*
-	 * We need to sample the current value to convert the new
-	 * value from to relative and absolute, and to convert the
-	 * old value from absolute to relative.  To set a process
-	 * timer, we need a sample to balance the thread expiry
-	 * times (in arm_timer).  With an absolute time, we must
-	 * check if it's already passed.  In short, we need a sample.
+	 * Sample the current clock for saving the previous setting
+	 * and for rearming the timer.
 	 */
 	if (CPUCLOCK_PERTHREAD(timer->it_clock))
-		val = cpu_clock_sample(clkid, p);
+		now = cpu_clock_sample(clkid, p);
 	else
-		val = cpu_clock_sample_group(clkid, p, true);
+		now = cpu_clock_sample_group(clkid, p, !sigev_none);
 
+	/* Retrieve the previous expiry value if requested. */
 	if (old) {
-		if (old_expires == 0) {
-			old->it_value.tv_sec = 0;
-			old->it_value.tv_nsec = 0;
-		} else {
-			/*
-			 * Update the timer in case it has overrun already.
-			 * If it has, we'll report it as having overrun and
-			 * with the next reloaded timer already ticking,
-			 * though we are swallowing that pending
-			 * notification here to install the new setting.
-			 */
-			u64 exp = bump_cpu_timer(timer, val);
-
-			if (val < exp) {
-				old_expires = exp - val;
-				old->it_value = ns_to_timespec64(old_expires);
-			} else {
-				old->it_value.tv_nsec = 1;
-				old->it_value.tv_sec = 0;
-			}
-		}
+		old->it_value = (struct timespec64){ };
+		if (old_expires)
+			__posix_cpu_timer_get(timer, old, now);
 	}
 
+	/* Retry if the timer expiry is running concurrently */
 	if (unlikely(ret)) {
-		/*
-		 * We are colliding with the timer actually firing.
-		 * Punt after filling in the timer's old value, and
-		 * disable this firing since we are already reporting
-		 * it as an overrun (thanks to bump_cpu_timer above).
-		 */
 		unlock_task_sighand(p, &flags);
 		goto out;
 	}
 
-	if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
-		new_expires += val;
-	}
+	/* Convert relative expiry time to absolute */
+	if (new_expires && !(timer_flags & TIMER_ABSTIME))
+		new_expires += now;
+
+	/* 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. In case the timer is not
+	 * armed, enforce the reevaluation of the timer base so that the
+	 * process wide cputime counter can be disabled eventually.
 	 */
-	cpu_timer_setexpires(ctmr, new_expires);
-	if (new_expires != 0 && val < new_expires) {
-		arm_timer(timer, p);
+	if (likely(!sigev_none)) {
+		if (new_expires && now < new_expires)
+			arm_timer(timer, p);
+		else
+			trigger_base_recalc_expires(timer, p);
 	}
 
 	unlock_task_sighand(p, &flags);
+
+	posix_timer_set_common(timer, new);
+
 	/*
-	 * Install the new reload setting, and
-	 * set up the signal and overrun bookkeeping.
+	 * If the new expiry time was already in the past the timer was not
+	 * queued. Fire it immediately even if the thread never runs to
+	 * accumulate more time on this clock.
 	 */
-	timer->it_interval = timespec64_to_ktime(new->it_interval);
+	if (!sigev_none && new_expires && now >= new_expires)
+		cpu_timer_fire(timer);
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
+static void __posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp, u64 now)
+{
+	bool sigev_none = timer->it_sigev_notify == SIGEV_NONE;
+	u64 expires, iv = timer->it_interval;
 
 	/*
-	 * This acts as a modification timestamp for the timer,
-	 * so any automatic reload attempt will punt on seeing
-	 * that we have reset the timer manually.
+	 * Make sure that interval timers are moved forward for the
+	 * following cases:
+	 *  - SIGEV_NONE timers which are never armed
+	 *  - Timers which expired, but the signal has not yet been
+	 *    delivered
 	 */
-	timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
-		~REQUEUE_PENDING;
-	timer->it_overrun_last = 0;
-	timer->it_overrun = -1;
-
-	if (val >= new_expires) {
-		if (new_expires != 0) {
-			/*
-			 * The designated time already passed, so we notify
-			 * immediately, even if the thread never runs to
-			 * accumulate more time on this clock.
-			 */
-			cpu_timer_fire(timer);
-		}
+	if (iv && ((timer->it_requeue_pending & REQUEUE_PENDING) || sigev_none))
+		expires = bump_cpu_timer(timer, now);
+	else
+		expires = cpu_timer_getexpires(&timer->it.cpu);
 
+	/*
+	 * Expired interval timers cannot have a remaining time <= 0.
+	 * The kernel has to move them forward so that the next
+	 * timer expiry is > @now.
+	 */
+	if (now < expires) {
+		itp->it_value = ns_to_timespec64(expires - now);
+	} else {
 		/*
-		 * Make sure we don't keep around the process wide cputime
-		 * counter or the tick dependency if they are not necessary.
+		 * A single shot SIGEV_NONE timer must return 0, when it is
+		 * expired! Timers which have a real signal delivery mode
+		 * must return a remaining time greater than 0 because the
+		 * signal has not yet been delivered.
 		 */
-		sighand = lock_task_sighand(p, &flags);
-		if (!sighand)
-			goto out;
-
-		if (!cpu_timer_queued(ctmr))
-			trigger_base_recalc_expires(timer, p);
-
-		unlock_task_sighand(p, &flags);
+		if (!sigev_none)
+			itp->it_value.tv_nsec = 1;
 	}
- out:
-	rcu_read_unlock();
-	if (old)
-		old->it_interval = ns_to_timespec64(old_incr);
-
-	return ret;
 }
 
 static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
 {
 	clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
-	struct cpu_timer *ctmr = &timer->it.cpu;
-	u64 now, expires = cpu_timer_getexpires(ctmr);
 	struct task_struct *p;
+	u64 now;
 
 	rcu_read_lock();
 	p = cpu_timer_task_rcu(timer);
-	if (!p)
-		goto out;
+	if (p && cpu_timer_getexpires(&timer->it.cpu)) {
+		itp->it_interval = ktime_to_timespec64(timer->it_interval);
 
-	/*
-	 * Easy part: convert the reload time.
-	 */
-	itp->it_interval = ktime_to_timespec64(timer->it_interval);
-
-	if (!expires)
-		goto out;
-
-	/*
-	 * Sample the clock to take the difference with the expiry time.
-	 */
-	if (CPUCLOCK_PERTHREAD(timer->it_clock))
-		now = cpu_clock_sample(clkid, p);
-	else
-		now = cpu_clock_sample_group(clkid, p, false);
+		if (CPUCLOCK_PERTHREAD(timer->it_clock))
+			now = cpu_clock_sample(clkid, p);
+		else
+			now = cpu_clock_sample_group(clkid, p, false);
 
-	if (now < expires) {
-		itp->it_value = ns_to_timespec64(expires - now);
-	} else {
-		/*
-		 * The timer should have expired already, but the firing
-		 * hasn't taken place yet.  Say it's just about to expire.
-		 */
-		itp->it_value.tv_nsec = 1;
-		itp->it_value.tv_sec = 0;
+		__posix_cpu_timer_get(timer, itp, now);
 	}
-out:
 	rcu_read_unlock();
 }
 

kernel/time/posix-timers.c

@@ -277,10 +277,17 @@ void posixtimer_rearm(struct kernel_siginfo *info)
 	unlock_timer(timr, flags);
 }
 
-int posix_timer_event(struct k_itimer *timr, int si_private)
+int posix_timer_queue_signal(struct k_itimer *timr)
 {
+	int ret, si_private = 0;
 	enum pid_type type;
-	int ret;
+
+	lockdep_assert_held(&timr->it_lock);
+
+	timr->it_active = 0;
+	if (timr->it_interval)
+		si_private = ++timr->it_requeue_pending;
+
 	/*
 	 * FIXME: if ->sigq is queued we can race with
 	 * dequeue_signal()->posixtimer_rearm().
@@ -309,19 +316,13 @@ int posix_timer_event(struct k_itimer *timr, int si_private)
  */
 static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
 {
+	struct k_itimer *timr = container_of(timer, struct k_itimer, it.real.timer);
 	enum hrtimer_restart ret = HRTIMER_NORESTART;
-	struct k_itimer *timr;
 	unsigned long flags;
-	int si_private = 0;
 
-	timr = container_of(timer, struct k_itimer, it.real.timer);
 	spin_lock_irqsave(&timr->it_lock, flags);
 
-	timr->it_active = 0;
-	if (timr->it_interval != 0)
-		si_private = ++timr->it_requeue_pending;
-
-	if (posix_timer_event(timr, si_private)) {
+	if (posix_timer_queue_signal(timr)) {
 		/*
 		 * The signal was not queued due to SIG_IGN. As a
 		 * consequence the timer is not going to be rearmed from
@@ -515,7 +516,7 @@ static int do_timer_create(clockid_t which_clock, struct sigevent *event,
 	spin_lock_irq(&current->sighand->siglock);
 	/* This makes the timer valid in the hash table */
 	WRITE_ONCE(new_timer->it_signal, current->signal);
-	list_add(&new_timer->list, &current->signal->posix_timers);
+	hlist_add_head(&new_timer->list, &current->signal->posix_timers);
 	spin_unlock_irq(&current->sighand->siglock);
 	/*
 	 * After unlocking sighand::siglock @new_timer is subject to
@@ -856,6 +857,23 @@ static struct k_itimer *timer_wait_running(struct k_itimer *timer,
 	return lock_timer(timer_id, flags);
 }
 
+/*
+ * Set up the new interval and reset the signal delivery data
+ */
+void posix_timer_set_common(struct k_itimer *timer, struct itimerspec64 *new_setting)
+{
+	if (new_setting->it_value.tv_sec || new_setting->it_value.tv_nsec)
+		timer->it_interval = timespec64_to_ktime(new_setting->it_interval);
+	else
+		timer->it_interval = 0;
+
+	/* Prevent reloading in case there is a signal pending */
+	timer->it_requeue_pending = (timer->it_requeue_pending + 2) & ~REQUEUE_PENDING;
+	/* Reset overrun accounting */
+	timer->it_overrun_last = 0;
+	timer->it_overrun = -1LL;
+}
+
 /* Set a POSIX.1b interval timer. */
 int common_timer_set(struct k_itimer *timr, int flags,
 		     struct itimerspec64 *new_setting,
@@ -878,15 +896,12 @@ int common_timer_set(struct k_itimer *timr, int flags,
 		return TIMER_RETRY;
 
 	timr->it_active = 0;
-	timr->it_requeue_pending = (timr->it_requeue_pending + 2) &
-		~REQUEUE_PENDING;
-	timr->it_overrun_last = 0;
+	posix_timer_set_common(timr, new_setting);
 
-	/* Switch off the timer when it_value is zero */
+	/* Keep timer disarmed when it_value is zero */
 	if (!new_setting->it_value.tv_sec && !new_setting->it_value.tv_nsec)
 		return 0;
 
-	timr->it_interval = timespec64_to_ktime(new_setting->it_interval);
 	expires = timespec64_to_ktime(new_setting->it_value);
 	if (flags & TIMER_ABSTIME)
 		expires = timens_ktime_to_host(timr->it_clock, expires);
@@ -904,7 +919,7 @@ static int do_timer_settime(timer_t timer_id, int tmr_flags,
 	const struct k_clock *kc;
 	struct k_itimer *timr;
 	unsigned long flags;
-	int error = 0;
+	int error;
 
 	if (!timespec64_valid(&new_spec64->it_interval) ||
 	    !timespec64_valid(&new_spec64->it_value))
@@ -918,6 +933,9 @@ static int do_timer_settime(timer_t timer_id, int tmr_flags,
 	if (!timr)
 		return -EINVAL;
 
+	if (old_spec64)
+		old_spec64->it_interval = ktime_to_timespec64(timr->it_interval);
+
 	kc = timr->kclock;
 	if (WARN_ON_ONCE(!kc || !kc->timer_set))
 		error = -EINVAL;
@@ -1021,7 +1039,7 @@ SYSCALL_DEFINE1(timer_delete, timer_t, timer_id)
 	}
 
 	spin_lock(&current->sighand->siglock);
-	list_del(&timer->list);
+	hlist_del(&timer->list);
 	spin_unlock(&current->sighand->siglock);
 	/*
 	 * A concurrent lookup could check timer::it_signal lockless. It
@@ -1071,7 +1089,7 @@ static void itimer_delete(struct k_itimer *timer)
 
 		goto retry_delete;
 	}
-	list_del(&timer->list);
+	hlist_del(&timer->list);
 
 	/*
 	 * Setting timer::it_signal to NULL is technically not required
@@ -1092,22 +1110,19 @@ static void itimer_delete(struct k_itimer *timer)
  */
 void exit_itimers(struct task_struct *tsk)
 {
-	struct list_head timers;
-	struct k_itimer *tmr;
+	struct hlist_head timers;
 
-	if (list_empty(&tsk->signal->posix_timers))
+	if (hlist_empty(&tsk->signal->posix_timers))
 		return;
 
 	/* Protect against concurrent read via /proc/$PID/timers */
 	spin_lock_irq(&tsk->sighand->siglock);
-	list_replace_init(&tsk->signal->posix_timers, &timers);
+	hlist_move_list(&tsk->signal->posix_timers, &timers);
 	spin_unlock_irq(&tsk->sighand->siglock);
 
 	/* The timers are not longer accessible via tsk::signal */
-	while (!list_empty(&timers)) {
-		tmr = list_first_entry(&timers, struct k_itimer, list);
-		itimer_delete(tmr);
-	}
+	while (!hlist_empty(&timers))
+		itimer_delete(hlist_entry(timers.first, struct k_itimer, list));
 }
 
 SYSCALL_DEFINE2(clock_settime, const clockid_t, which_clock,

kernel/time/posix-timers.h

@@ -36,10 +36,11 @@ extern const struct k_clock clock_process;
 extern const struct k_clock clock_thread;
 extern const struct k_clock alarm_clock;
 
-int posix_timer_event(struct k_itimer *timr, int si_private);
+int posix_timer_queue_signal(struct k_itimer *timr);
 
 void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting);
 int common_timer_set(struct k_itimer *timr, int flags,
 		     struct itimerspec64 *new_setting,
 		     struct itimerspec64 *old_setting);
+void posix_timer_set_common(struct k_itimer *timer, struct itimerspec64 *new_setting);
 int common_timer_del(struct k_itimer *timer);