From: Anna-Maria Gleixner <anna-maria@linutronix.de>
Date: Mon, 27 May 2019 16:54:06 +0200
Subject: [PATCH] posix-timers: Add expiry lock
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Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: da77ceac3d20f27310a07a7c346a4ee6b40d6c28
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

If a about to be removed posix timer is active then the code will retry the
delete operation until it succeeds / the timer callback completes.

Use hrtimer_grab_expiry_lock() for posix timers which use a hrtimer underneath
to spin on a lock until the callback finished.

Introduce cpu_timers_grab_expiry_lock() for the posix-cpu-timer. This will
acquire the proper per-CPU spin_lock which is acquired by the CPU which is
expirering the timer.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
[bigeasy: keep the posix-cpu timer bits, everything else got applied]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
 include/linux/posix-timers.h   |    1 +
 kernel/time/posix-cpu-timers.c |   28 +++++++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -72,6 +72,7 @@ struct cpu_timer {
 	struct task_struct	*task;
 	struct list_head	elist;
 	int			firing;
+	int			firing_cpu;
 };
 
 static inline bool cpu_timer_enqueue(struct timerqueue_head *head,
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -475,6 +475,20 @@ static int posix_cpu_timer_del(struct k_
 	return ret;
 }
 
+static DEFINE_PER_CPU(spinlock_t, cpu_timer_expiry_lock) = __SPIN_LOCK_UNLOCKED(cpu_timer_expiry_lock);
+
+static void posix_cpu_wait_running(struct k_itimer *timer)
+{
+	int cpu = timer->it.cpu.firing_cpu;
+
+	if (cpu >= 0) {
+		spinlock_t *expiry_lock = per_cpu_ptr(&cpu_timer_expiry_lock, cpu);
+
+		spin_lock_irq(expiry_lock);
+		spin_unlock_irq(expiry_lock);
+	}
+}
+
 static void cleanup_timerqueue(struct timerqueue_head *head)
 {
 	struct timerqueue_node *node;
@@ -812,6 +826,7 @@ static u64 collect_timerqueue(struct tim
 			return expires;
 
 		ctmr->firing = 1;
+		ctmr->firing_cpu = smp_processor_id();
 		cpu_timer_dequeue(ctmr);
 		list_add_tail(&ctmr->elist, firing);
 	}
@@ -1150,6 +1165,7 @@ static void __run_posix_cpu_timers(struc
 {
 	struct k_itimer *timer, *next;
 	unsigned long flags;
+	spinlock_t *expiry_lock;
 	LIST_HEAD(firing);
 
 	/*
@@ -1159,8 +1175,13 @@ static void __run_posix_cpu_timers(struc
 	if (!fastpath_timer_check(tsk))
 		return;
 
-	if (!lock_task_sighand(tsk, &flags))
+	expiry_lock = this_cpu_ptr(&cpu_timer_expiry_lock);
+	spin_lock(expiry_lock);
+
+	if (!lock_task_sighand(tsk, &flags)) {
+		spin_unlock(expiry_lock);
 		return;
+	}
 	/*
 	 * Here we take off tsk->signal->cpu_timers[N] and
 	 * tsk->cpu_timers[N] all the timers that are firing, and
@@ -1193,6 +1214,7 @@ static void __run_posix_cpu_timers(struc
 		list_del_init(&timer->it.cpu.elist);
 		cpu_firing = timer->it.cpu.firing;
 		timer->it.cpu.firing = 0;
+		timer->it.cpu.firing_cpu = -1;
 		/*
 		 * The firing flag is -1 if we collided with a reset
 		 * of the timer, which already reported this
@@ -1202,6 +1224,7 @@ static void __run_posix_cpu_timers(struc
 			cpu_timer_fire(timer);
 		spin_unlock(&timer->it_lock);
 	}
+	spin_unlock(expiry_lock);
 }
 
 #ifdef CONFIG_PREEMPT_RT
@@ -1464,6 +1487,8 @@ static int do_cpu_nanosleep(const clocki
 		spin_unlock_irq(&timer.it_lock);
 
 		while (error == TIMER_RETRY) {
+
+			posix_cpu_wait_running(&timer);
 			/*
 			 * We need to handle case when timer was or is in the
 			 * middle of firing. In other cases we already freed
@@ -1582,6 +1607,7 @@ const struct k_clock clock_posix_cpu = {
 	.timer_del		= posix_cpu_timer_del,
 	.timer_get		= posix_cpu_timer_get,
 	.timer_rearm		= posix_cpu_timer_rearm,
+	.timer_wait_running	= posix_cpu_wait_running,
 };
 
 const struct k_clock clock_process = {