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From: John Stultz <johnstul@us.ibm.com>
Date: Fri, 3 Jul 2009 08:29:58 -0500
Subject: posix-timers: Thread posix-cpu-timers on -rt
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.10-rt8.tar.xz
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(-)
--- 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: */
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -50,6 +50,12 @@ static struct sighand_struct init_sighan
.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),
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1575,6 +1575,9 @@ static void rt_mutex_init_task(struct ta
*/
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;
--- 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"
@@ -1135,14 +1138,12 @@ static inline int fastpath_timer_check(s
* 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.
@@ -1195,6 +1196,153 @@ void run_posix_cpu_timers(struct task_st
}
}
+#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.
|
