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linux/debian/patches-rt/0099-hrtimers-Prepare-full-...

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From 116fd08767bc0bfe1df50417612622aa46928199 Mon Sep 17 00:00:00 2001
Message-Id: <116fd08767bc0bfe1df50417612622aa46928199.1599166690.git.zanussi@kernel.org>
In-Reply-To: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
References: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:29:34 -0500
Subject: [PATCH 099/333] hrtimers: Prepare full preemption
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.142-rt63.tar.xz
Make cancellation of a running callback in softirq context safe
against preemption.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
fs/timerfd.c | 5 ++++-
include/linux/hrtimer.h | 13 +++++++++++-
include/linux/posix-timers.h | 2 +-
kernel/time/alarmtimer.c | 2 +-
kernel/time/hrtimer.c | 33 +++++++++++++++++++++++++++++-
kernel/time/itimer.c | 1 +
kernel/time/posix-timers.c | 39 ++++++++++++++++++++++++++++++++++--
7 files changed, 88 insertions(+), 7 deletions(-)
diff --git a/fs/timerfd.c b/fs/timerfd.c
index d69ad801eb80..82d0f52414a6 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -471,7 +471,10 @@ static int do_timerfd_settime(int ufd, int flags,
break;
}
spin_unlock_irq(&ctx->wqh.lock);
- cpu_relax();
+ if (isalarm(ctx))
+ hrtimer_wait_for_timer(&ctx->t.alarm.timer);
+ else
+ hrtimer_wait_for_timer(&ctx->t.tmr);
}
/*
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index cbd041b22088..8714f1a37d84 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -22,6 +22,7 @@
#include <linux/percpu.h>
#include <linux/timer.h>
#include <linux/timerqueue.h>
+#include <linux/wait.h>
struct hrtimer_clock_base;
struct hrtimer_cpu_base;
@@ -216,6 +217,9 @@ struct hrtimer_cpu_base {
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;
@@ -433,6 +437,13 @@ static inline void hrtimer_restart(struct hrtimer *timer)
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);
@@ -464,7 +475,7 @@ static inline bool hrtimer_is_queued(struct hrtimer *timer)
* Helper function to check, whether the timer is running the callback
* function
*/
-static inline int hrtimer_callback_running(struct hrtimer *timer)
+static inline int hrtimer_callback_running(const struct hrtimer *timer)
{
return timer->base->running == timer;
}
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index ee7e987ea1b4..0571b498db73 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -114,8 +114,8 @@ struct k_itimer {
struct {
struct alarm alarmtimer;
} alarm;
- struct rcu_head rcu;
} it;
+ struct rcu_head rcu;
};
void run_posix_cpu_timers(struct task_struct *task);
diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 9eece67f29f3..a465564367ec 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -438,7 +438,7 @@ int alarm_cancel(struct alarm *alarm)
int ret = alarm_try_to_cancel(alarm);
if (ret >= 0)
return ret;
- cpu_relax();
+ hrtimer_wait_for_timer(&alarm->timer);
}
}
EXPORT_SYMBOL_GPL(alarm_cancel);
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index c6f755495a63..e135cb27db39 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -939,6 +939,33 @@ u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
}
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)
+{
+ 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)));
+}
+
+#else
+# define wake_up_timer_waiters(b) do { } while (0)
+#endif
+
/*
* enqueue_hrtimer - internal function to (re)start a timer
*
@@ -1174,7 +1201,7 @@ int hrtimer_cancel(struct hrtimer *timer)
if (ret >= 0)
return ret;
- cpu_relax();
+ hrtimer_wait_for_timer(timer);
}
}
EXPORT_SYMBOL_GPL(hrtimer_cancel);
@@ -1480,6 +1507,7 @@ static __latent_entropy void hrtimer_run_softirq(struct softirq_action *h)
hrtimer_update_softirq_timer(cpu_base, true);
raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
+ wake_up_timer_waiters(cpu_base);
}
#ifdef CONFIG_HIGH_RES_TIMERS
@@ -1849,6 +1877,9 @@ int hrtimers_prepare_cpu(unsigned int cpu)
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
return 0;
}
diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
index 9a65713c8309..55b0e58368bf 100644
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -215,6 +215,7 @@ int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
/* 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);
goto again;
}
expires = timeval_to_ktime(value->it_value);
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 5a01c4fdbfef..a5ec421e3437 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -463,7 +463,7 @@ static struct k_itimer * alloc_posix_timer(void)
static void k_itimer_rcu_free(struct rcu_head *head)
{
- struct k_itimer *tmr = container_of(head, struct k_itimer, it.rcu);
+ struct k_itimer *tmr = container_of(head, struct k_itimer, rcu);
kmem_cache_free(posix_timers_cache, tmr);
}
@@ -480,7 +480,7 @@ static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
}
put_pid(tmr->it_pid);
sigqueue_free(tmr->sigq);
- call_rcu(&tmr->it.rcu, k_itimer_rcu_free);
+ call_rcu(&tmr->rcu, k_itimer_rcu_free);
}
static int common_timer_create(struct k_itimer *new_timer)
@@ -821,6 +821,22 @@ static void common_hrtimer_arm(struct k_itimer *timr, ktime_t expires,
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)
+{
+#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
+}
+
static int common_hrtimer_try_to_cancel(struct k_itimer *timr)
{
return hrtimer_try_to_cancel(&timr->it.real.timer);
@@ -885,6 +901,7 @@ static int do_timer_settime(timer_t timer_id, int flags,
if (!timr)
return -EINVAL;
+ rcu_read_lock();
kc = timr->kclock;
if (WARN_ON_ONCE(!kc || !kc->timer_set))
error = -EINVAL;
@@ -893,9 +910,12 @@ static int do_timer_settime(timer_t timer_id, int flags,
unlock_timer(timr, flag);
if (error == TIMER_RETRY) {
+ timer_wait_for_callback(kc, timr);
old_spec64 = NULL; // We already got the old time...
+ rcu_read_unlock();
goto retry;
}
+ rcu_read_unlock();
return error;
}
@@ -977,10 +997,15 @@ SYSCALL_DEFINE1(timer_delete, timer_t, timer_id)
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();
goto retry_delete;
}
+ rcu_read_unlock();
spin_lock(&current->sighand->siglock);
list_del(&timer->list);
@@ -1006,8 +1031,18 @@ static void itimer_delete(struct k_itimer *timer)
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();
goto retry_delete;
}
list_del(&timer->list);
--
2.17.1
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