From f7d44ae1ff53ff9277b2207c7987b8ffa0a65738 Mon Sep 17 00:00:00 2001
From: John Stultz <johnstul@us.ibm.com>
Date: Fri, 3 Jul 2009 08:29:58 -0500
Subject: [PATCH 105/283] posix-timers: Thread posix-cpu-timers on -rt

posix-cpu-timer code takes non -rt safe locks in hard irq
context. Move it to a thread.

[ 3.0 fixes from Peter Zijlstra <peterz@infradead.org> ]

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/sched.h          |   3 +
 init/init_task.c               |   7 ++
 kernel/fork.c                  |   3 +
 kernel/time/posix-cpu-timers.c | 154 ++++++++++++++++++++++++++++++++-
 4 files changed, 164 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 535e57775208..c2dfe6939773 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -832,6 +832,9 @@ struct task_struct {
 #ifdef CONFIG_POSIX_TIMERS
 	struct task_cputime		cputime_expires;
 	struct list_head		cpu_timers[3];
+#ifdef CONFIG_PREEMPT_RT_BASE
+	struct task_struct		*posix_timer_list;
+#endif
 #endif
 
 	/* Process credentials: */
diff --git a/init/init_task.c b/init/init_task.c
index 0b49b9cf5571..9e3362748214 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -50,6 +50,12 @@ static struct sighand_struct init_sighand = {
 	.signalfd_wqh	= __WAIT_QUEUE_HEAD_INITIALIZER(init_sighand.signalfd_wqh),
 };
 
+#if defined(CONFIG_POSIX_TIMERS) && defined(CONFIG_PREEMPT_RT_BASE)
+# define INIT_TIMER_LIST		.posix_timer_list = NULL,
+#else
+# define INIT_TIMER_LIST
+#endif
+
 /*
  * Set up the first task table, touch at your own risk!. Base=0,
  * limit=0x1fffff (=2MB)
@@ -119,6 +125,7 @@ struct task_struct init_task
 	INIT_CPU_TIMERS(init_task)
 	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
 	.timer_slack_ns = 50000, /* 50 usec default slack */
+	INIT_TIMER_LIST
 	.thread_pid	= &init_struct_pid,
 	.thread_group	= LIST_HEAD_INIT(init_task.thread_group),
 	.thread_node	= LIST_HEAD_INIT(init_signals.thread_head),
diff --git a/kernel/fork.c b/kernel/fork.c
index 98c971cb1d36..492bc898b09a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1585,6 +1585,9 @@ static void rt_mutex_init_task(struct task_struct *p)
  */
 static void posix_cpu_timers_init(struct task_struct *tsk)
 {
+#ifdef CONFIG_PREEMPT_RT_BASE
+	tsk->posix_timer_list = NULL;
+#endif
 	tsk->cputime_expires.prof_exp = 0;
 	tsk->cputime_expires.virt_exp = 0;
 	tsk->cputime_expires.sched_exp = 0;
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 76801b9b481e..baeeaef3b721 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -3,8 +3,10 @@
  * Implement CPU time clocks for the POSIX clock interface.
  */
 
+#include <uapi/linux/sched/types.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/cputime.h>
+#include <linux/sched/rt.h>
 #include <linux/posix-timers.h>
 #include <linux/errno.h>
 #include <linux/math64.h>
@@ -15,6 +17,7 @@
 #include <linux/workqueue.h>
 #include <linux/compat.h>
 #include <linux/sched/deadline.h>
+#include <linux/smpboot.h>
 
 #include "posix-timers.h"
 
@@ -1136,14 +1139,12 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
  * already updated our counts.  We need to check if any timers fire now.
  * Interrupts are disabled.
  */
-void run_posix_cpu_timers(struct task_struct *tsk)
+static void __run_posix_cpu_timers(struct task_struct *tsk)
 {
 	LIST_HEAD(firing);
 	struct k_itimer *timer, *next;
 	unsigned long flags;
 
-	lockdep_assert_irqs_disabled();
-
 	/*
 	 * The fast path checks that there are no expired thread or thread
 	 * group timers.  If that's so, just return.
@@ -1196,6 +1197,153 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 	}
 }
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+#include <linux/kthread.h>
+#include <linux/cpu.h>
+DEFINE_PER_CPU(struct task_struct *, posix_timer_task);
+DEFINE_PER_CPU(struct task_struct *, posix_timer_tasklist);
+DEFINE_PER_CPU(bool, posix_timer_th_active);
+
+static void posix_cpu_kthread_fn(unsigned int cpu)
+{
+	struct task_struct *tsk = NULL;
+	struct task_struct *next = NULL;
+
+	BUG_ON(per_cpu(posix_timer_task, cpu) != current);
+
+	/* grab task list */
+	raw_local_irq_disable();
+	tsk = per_cpu(posix_timer_tasklist, cpu);
+	per_cpu(posix_timer_tasklist, cpu) = NULL;
+	raw_local_irq_enable();
+
+	/* its possible the list is empty, just return */
+	if (!tsk)
+		return;
+
+	/* Process task list */
+	while (1) {
+		/* save next */
+		next = tsk->posix_timer_list;
+
+		/* run the task timers, clear its ptr and
+		 * unreference it
+		 */
+		__run_posix_cpu_timers(tsk);
+		tsk->posix_timer_list = NULL;
+		put_task_struct(tsk);
+
+		/* check if this is the last on the list */
+		if (next == tsk)
+			break;
+		tsk = next;
+	}
+}
+
+static inline int __fastpath_timer_check(struct task_struct *tsk)
+{
+	/* tsk == current, ensure it is safe to use ->signal/sighand */
+	if (unlikely(tsk->exit_state))
+		return 0;
+
+	if (!task_cputime_zero(&tsk->cputime_expires))
+			return 1;
+
+	if (!task_cputime_zero(&tsk->signal->cputime_expires))
+			return 1;
+
+	return 0;
+}
+
+void run_posix_cpu_timers(struct task_struct *tsk)
+{
+	unsigned int cpu = smp_processor_id();
+	struct task_struct *tasklist;
+
+	BUG_ON(!irqs_disabled());
+
+	if (per_cpu(posix_timer_th_active, cpu) != true)
+		return;
+
+	/* get per-cpu references */
+	tasklist = per_cpu(posix_timer_tasklist, cpu);
+
+	/* check to see if we're already queued */
+	if (!tsk->posix_timer_list && __fastpath_timer_check(tsk)) {
+		get_task_struct(tsk);
+		if (tasklist) {
+			tsk->posix_timer_list = tasklist;
+		} else {
+			/*
+			 * The list is terminated by a self-pointing
+			 * task_struct
+			 */
+			tsk->posix_timer_list = tsk;
+		}
+		per_cpu(posix_timer_tasklist, cpu) = tsk;
+
+		wake_up_process(per_cpu(posix_timer_task, cpu));
+	}
+}
+
+static int posix_cpu_kthread_should_run(unsigned int cpu)
+{
+	return __this_cpu_read(posix_timer_tasklist) != NULL;
+}
+
+static void posix_cpu_kthread_park(unsigned int cpu)
+{
+	this_cpu_write(posix_timer_th_active, false);
+}
+
+static void posix_cpu_kthread_unpark(unsigned int cpu)
+{
+	this_cpu_write(posix_timer_th_active, true);
+}
+
+static void posix_cpu_kthread_setup(unsigned int cpu)
+{
+	struct sched_param sp;
+
+	sp.sched_priority = MAX_RT_PRIO - 1;
+	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+	posix_cpu_kthread_unpark(cpu);
+}
+
+static struct smp_hotplug_thread posix_cpu_thread = {
+	.store			= &posix_timer_task,
+	.thread_should_run	= posix_cpu_kthread_should_run,
+	.thread_fn		= posix_cpu_kthread_fn,
+	.thread_comm		= "posixcputmr/%u",
+	.setup			= posix_cpu_kthread_setup,
+	.park			= posix_cpu_kthread_park,
+	.unpark			= posix_cpu_kthread_unpark,
+};
+
+static int __init posix_cpu_thread_init(void)
+{
+	/* Start one for boot CPU. */
+	unsigned long cpu;
+	int ret;
+
+	/* init the per-cpu posix_timer_tasklets */
+	for_each_possible_cpu(cpu)
+		per_cpu(posix_timer_tasklist, cpu) = NULL;
+
+	ret = smpboot_register_percpu_thread(&posix_cpu_thread);
+	WARN_ON(ret);
+
+	return 0;
+}
+early_initcall(posix_cpu_thread_init);
+#else /* CONFIG_PREEMPT_RT_BASE */
+void run_posix_cpu_timers(struct task_struct *tsk)
+{
+	lockdep_assert_irqs_disabled();
+	__run_posix_cpu_timers(tsk);
+}
+#endif /* CONFIG_PREEMPT_RT_BASE */
+
 /*
  * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
  * The tsk->sighand->siglock must be held by the caller.
-- 
2.20.1

