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From 50c77b51735c142605d4621a971453a3705eb233 Mon Sep 17 00:00:00 2001
Message-Id: <50c77b51735c142605d4621a971453a3705eb233.1596234184.git.zanussi@kernel.org>
In-Reply-To: <378ee68279f6a7631221f2670a9298620148690d.1596234183.git.zanussi@kernel.org>
References: <378ee68279f6a7631221f2670a9298620148690d.1596234183.git.zanussi@kernel.org>
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 24 Jun 2019 19:39:06 +0200
Subject: [PATCH 271/329] timers: Redo the notification of canceling timers on
-RT
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.135-rt60.tar.xz
[ Upstream commit c71273154c2ad12e13333aada340ff30e826a11b ]
Rework of the hrtimer, timer and posix-timer cancelation interface
on -RT. Instead of the swait/schedule interface we now have locks
which are taken while timer is active. During the cancellation of an
active timer the lock is acquired. The lock will then either
PI-boost the timer or block and wait until the timer completed.
The new code looks simpler and does not trigger a warning from
rcu_note_context_switch() anymore like reported by Grygorii Strashko
and Daniel Wagner.
The patches were contributed by Anna-Maria Gleixner.
This is an all in one commit of the following patches:
| [PATCH] timers: Introduce expiry spin lock
| [PATCH] timers: Drop expiry lock after each timer invocation
| [PATCH] hrtimer: Introduce expiry spin lock
| [PATCH] posix-timers: move rcu out of union
| [PATCH] posix-timers: Add expiry lock
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
fs/timerfd.c | 5 +-
include/linux/hrtimer.h | 17 ++----
include/linux/posix-timers.h | 1 +
kernel/time/alarmtimer.c | 2 +-
kernel/time/hrtimer.c | 36 ++++---------
kernel/time/itimer.c | 2 +-
kernel/time/posix-cpu-timers.c | 23 ++++++++
kernel/time/posix-timers.c | 69 ++++++++++--------------
kernel/time/posix-timers.h | 2 +
kernel/time/timer.c | 96 ++++++++++++++++------------------
10 files changed, 118 insertions(+), 135 deletions(-)
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -471,10 +471,11 @@
break;
}
spin_unlock_irq(&ctx->wqh.lock);
+
if (isalarm(ctx))
- hrtimer_wait_for_timer(&ctx->t.alarm.timer);
+ hrtimer_grab_expiry_lock(&ctx->t.alarm.timer);
else
- hrtimer_wait_for_timer(&ctx->t.tmr);
+ hrtimer_grab_expiry_lock(&ctx->t.tmr);
}
/*
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -22,7 +22,6 @@
#include <linux/percpu.h>
#include <linux/timer.h>
#include <linux/timerqueue.h>
-#include <linux/wait.h>
struct hrtimer_clock_base;
struct hrtimer_cpu_base;
@@ -193,6 +192,8 @@
* @nr_retries: Total number of hrtimer interrupt retries
* @nr_hangs: Total number of hrtimer interrupt hangs
* @max_hang_time: Maximum time spent in hrtimer_interrupt
+ * @softirq_expiry_lock: Lock which is taken while softirq based hrtimer are
+ * expired
* @expires_next: absolute time of the next event, is required for remote
* hrtimer enqueue; it is the total first expiry time (hard
* and soft hrtimer are taken into account)
@@ -220,12 +221,10 @@
unsigned short nr_hangs;
unsigned int max_hang_time;
#endif
+ spinlock_t softirq_expiry_lock;
ktime_t expires_next;
struct hrtimer *next_timer;
ktime_t softirq_expires_next;
-#ifdef CONFIG_PREEMPT_RT_BASE
- wait_queue_head_t wait;
-#endif
struct hrtimer *softirq_next_timer;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
} ____cacheline_aligned;
@@ -426,6 +425,7 @@
extern int hrtimer_cancel(struct hrtimer *timer);
extern int hrtimer_try_to_cancel(struct hrtimer *timer);
+extern void hrtimer_grab_expiry_lock(const struct hrtimer *timer);
static inline void hrtimer_start_expires(struct hrtimer *timer,
enum hrtimer_mode mode)
@@ -443,13 +443,6 @@
hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
}
-/* Softirq preemption could deadlock timer removal */
-#ifdef CONFIG_PREEMPT_RT_BASE
- extern void hrtimer_wait_for_timer(const struct hrtimer *timer);
-#else
-# define hrtimer_wait_for_timer(timer) do { cpu_relax(); } while (0)
-#endif
-
/* Query timers: */
extern ktime_t __hrtimer_get_remaining(const struct hrtimer *timer, bool adjust);
@@ -481,7 +474,7 @@
* Helper function to check, whether the timer is running the callback
* function
*/
-static inline int hrtimer_callback_running(const struct hrtimer *timer)
+static inline int hrtimer_callback_running(struct hrtimer *timer)
{
return timer->base->running == timer;
}
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -15,6 +15,7 @@
u64 expires, incr;
struct task_struct *task;
int firing;
+ int firing_cpu;
};
/*
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -438,7 +438,7 @@
int ret = alarm_try_to_cancel(alarm);
if (ret >= 0)
return ret;
- hrtimer_wait_for_timer(&alarm->timer);
+ hrtimer_grab_expiry_lock(&alarm->timer);
}
}
EXPORT_SYMBOL_GPL(alarm_cancel);
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -963,33 +963,16 @@
}
EXPORT_SYMBOL_GPL(hrtimer_forward);
-#ifdef CONFIG_PREEMPT_RT_BASE
-# define wake_up_timer_waiters(b) wake_up(&(b)->wait)
-
-/**
- * hrtimer_wait_for_timer - Wait for a running timer
- *
- * @timer: timer to wait for
- *
- * The function waits in case the timers callback function is
- * currently executed on the waitqueue of the timer base. The
- * waitqueue is woken up after the timer callback function has
- * finished execution.
- */
-void hrtimer_wait_for_timer(const struct hrtimer *timer)
+void hrtimer_grab_expiry_lock(const struct hrtimer *timer)
{
struct hrtimer_clock_base *base = timer->base;
- if (base && base->cpu_base &&
- base->index >= HRTIMER_BASE_MONOTONIC_SOFT)
- wait_event(base->cpu_base->wait,
- !(hrtimer_callback_running(timer)));
+ if (base && base->cpu_base) {
+ spin_lock(&base->cpu_base->softirq_expiry_lock);
+ spin_unlock(&base->cpu_base->softirq_expiry_lock);
+ }
}
-#else
-# define wake_up_timer_waiters(b) do { } while (0)
-#endif
-
/*
* enqueue_hrtimer - internal function to (re)start a timer
*
@@ -1227,7 +1210,7 @@
if (ret >= 0)
return ret;
- hrtimer_wait_for_timer(timer);
+ hrtimer_grab_expiry_lock(timer);
}
}
EXPORT_SYMBOL_GPL(hrtimer_cancel);
@@ -1531,6 +1514,7 @@
unsigned long flags;
ktime_t now;
+ spin_lock(&cpu_base->softirq_expiry_lock);
raw_spin_lock_irqsave(&cpu_base->lock, flags);
now = hrtimer_update_base(cpu_base);
@@ -1540,7 +1524,7 @@
hrtimer_update_softirq_timer(cpu_base, true);
raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
- wake_up_timer_waiters(cpu_base);
+ spin_unlock(&cpu_base->softirq_expiry_lock);
}
#ifdef CONFIG_HIGH_RES_TIMERS
@@ -1950,9 +1934,7 @@
cpu_base->softirq_next_timer = NULL;
cpu_base->expires_next = KTIME_MAX;
cpu_base->softirq_expires_next = KTIME_MAX;
-#ifdef CONFIG_PREEMPT_RT_BASE
- init_waitqueue_head(&cpu_base->wait);
-#endif
+ spin_lock_init(&cpu_base->softirq_expiry_lock);
return 0;
}
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -215,7 +215,7 @@
/* We are sharing ->siglock with it_real_fn() */
if (hrtimer_try_to_cancel(timer) < 0) {
spin_unlock_irq(&tsk->sighand->siglock);
- hrtimer_wait_for_timer(&tsk->signal->real_timer);
+ hrtimer_grab_expiry_lock(timer);
goto again;
}
expires = timeval_to_ktime(value->it_value);
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -792,6 +792,7 @@
return t->expires;
t->firing = 1;
+ t->firing_cpu = smp_processor_id();
list_move_tail(&t->entry, firing);
}
@@ -1138,6 +1139,20 @@
return 0;
}
+static DEFINE_PER_CPU(spinlock_t, cpu_timer_expiry_lock) = __SPIN_LOCK_UNLOCKED(cpu_timer_expiry_lock);
+
+void cpu_timers_grab_expiry_lock(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);
+ }
+}
+
/*
* This is called from the timer interrupt handler. The irq handler has
* already updated our counts. We need to check if any timers fire now.
@@ -1148,6 +1163,7 @@
LIST_HEAD(firing);
struct k_itimer *timer, *next;
unsigned long flags;
+ spinlock_t *expiry_lock;
/*
* The fast path checks that there are no expired thread or thread
@@ -1156,6 +1172,9 @@
if (!fastpath_timer_check(tsk))
return;
+ expiry_lock = this_cpu_ptr(&cpu_timer_expiry_lock);
+ spin_lock(expiry_lock);
+
if (!lock_task_sighand(tsk, &flags))
return;
/*
@@ -1190,6 +1209,7 @@
list_del_init(&timer->it.cpu.entry);
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
@@ -1199,6 +1219,7 @@
cpu_timer_fire(timer);
spin_unlock(&timer->it_lock);
}
+ spin_unlock(expiry_lock);
}
#ifdef CONFIG_PREEMPT_RT_BASE
@@ -1466,6 +1487,8 @@
spin_unlock_irq(&timer.it_lock);
while (error == TIMER_RETRY) {
+
+ cpu_timers_grab_expiry_lock(&timer);
/*
* We need to handle case when timer was or is in the
* middle of firing. In other cases we already freed
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -821,25 +821,20 @@
hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
}
-/*
- * Protected by RCU!
- */
-static void timer_wait_for_callback(const struct k_clock *kc, struct k_itimer *timr)
+static int common_hrtimer_try_to_cancel(struct k_itimer *timr)
{
-#ifdef CONFIG_PREEMPT_RT_FULL
- if (kc->timer_arm == common_hrtimer_arm)
- hrtimer_wait_for_timer(&timr->it.real.timer);
- else if (kc == &alarm_clock)
- hrtimer_wait_for_timer(&timr->it.alarm.alarmtimer.timer);
- else
- /* FIXME: Whacky hack for posix-cpu-timers */
- schedule_timeout(1);
-#endif
+ return hrtimer_try_to_cancel(&timr->it.real.timer);
}
-static int common_hrtimer_try_to_cancel(struct k_itimer *timr)
+static void timer_wait_for_callback(const struct k_clock *kc, struct k_itimer *timer)
{
- return hrtimer_try_to_cancel(&timr->it.real.timer);
+ if (kc->timer_arm == common_hrtimer_arm)
+ hrtimer_grab_expiry_lock(&timer->it.real.timer);
+ else if (kc == &alarm_clock)
+ hrtimer_grab_expiry_lock(&timer->it.alarm.alarmtimer.timer);
+ else
+ /* posix-cpu-timers */
+ cpu_timers_grab_expiry_lock(timer);
}
/* Set a POSIX.1b interval timer. */
@@ -901,21 +896,21 @@
if (!timr)
return -EINVAL;
- rcu_read_lock();
kc = timr->kclock;
if (WARN_ON_ONCE(!kc || !kc->timer_set))
error = -EINVAL;
else
error = kc->timer_set(timr, flags, new_spec64, old_spec64);
- unlock_timer(timr, flag);
if (error == TIMER_RETRY) {
+ rcu_read_lock();
+ unlock_timer(timr, flag);
timer_wait_for_callback(kc, timr);
- old_spec64 = NULL; // We already got the old time...
rcu_read_unlock();
+ old_spec64 = NULL; // We already got the old time...
goto retry;
}
- rcu_read_unlock();
+ unlock_timer(timr, flag);
return error;
}
@@ -977,13 +972,21 @@
return 0;
}
-static inline int timer_delete_hook(struct k_itimer *timer)
+static int timer_delete_hook(struct k_itimer *timer)
{
const struct k_clock *kc = timer->kclock;
+ int ret;
if (WARN_ON_ONCE(!kc || !kc->timer_del))
return -EINVAL;
- return kc->timer_del(timer);
+ ret = kc->timer_del(timer);
+ if (ret == TIMER_RETRY) {
+ rcu_read_lock();
+ spin_unlock_irq(&timer->it_lock);
+ timer_wait_for_callback(kc, timer);
+ rcu_read_unlock();
+ }
+ return ret;
}
/* Delete a POSIX.1b interval timer. */
@@ -997,15 +1000,8 @@
if (!timer)
return -EINVAL;
- rcu_read_lock();
- if (timer_delete_hook(timer) == TIMER_RETRY) {
- unlock_timer(timer, flags);
- timer_wait_for_callback(clockid_to_kclock(timer->it_clock),
- timer);
- rcu_read_unlock();
+ if (timer_delete_hook(timer) == TIMER_RETRY)
goto retry_delete;
- }
- rcu_read_unlock();
spin_lock(&current->sighand->siglock);
list_del(&timer->list);
@@ -1031,20 +1027,9 @@
retry_delete:
spin_lock_irqsave(&timer->it_lock, flags);
- /* On RT we can race with a deletion */
- if (!timer->it_signal) {
- unlock_timer(timer, flags);
- return;
- }
-
- if (timer_delete_hook(timer) == TIMER_RETRY) {
- rcu_read_lock();
- unlock_timer(timer, flags);
- timer_wait_for_callback(clockid_to_kclock(timer->it_clock),
- timer);
- rcu_read_unlock();
+ if (timer_delete_hook(timer) == TIMER_RETRY)
goto retry_delete;
- }
+
list_del(&timer->list);
/*
* This keeps any tasks waiting on the spin lock from thinking
--- a/kernel/time/posix-timers.h
+++ b/kernel/time/posix-timers.h
@@ -32,6 +32,8 @@
extern const struct k_clock clock_thread;
extern const struct k_clock alarm_clock;
+extern void cpu_timers_grab_expiry_lock(struct k_itimer *timer);
+
int posix_timer_event(struct k_itimer *timr, int si_private);
void common_timer_get(struct k_itimer *timr, struct itimerspec64 *cur_setting);
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -45,7 +45,6 @@
#include <linux/slab.h>
#include <linux/compat.h>
#include <linux/random.h>
-#include <linux/swait.h>
#include <linux/uaccess.h>
#include <asm/unistd.h>
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