posix-timers: Convert timer list to hlist

No requirement for a real list. Spare a few bytes.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

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);

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;

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/time/posix-timers.c

@@ -515,7 +515,7 @@ 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
@@ -1025,7 +1025,7 @@ 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
@@ -1075,7 +1075,7 @@ 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
@@ -1096,22 +1096,19 @@ 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,