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-rw-r--r--include/linux/timer.h2
-rw-r--r--kernel/time/timer.c103
2 files changed, 96 insertions, 9 deletions
diff --git a/include/linux/timer.h b/include/linux/timer.h
index 282e4f2a532a..1e6650ed066d 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -183,7 +183,7 @@ extern void add_timer(struct timer_list *timer);
extern int try_to_del_timer_sync(struct timer_list *timer);
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
extern int del_timer_sync(struct timer_list *timer);
#else
# define del_timer_sync(t) del_timer(t)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 343c7ba33b1c..673c6a0f0c45 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -196,6 +196,10 @@ EXPORT_SYMBOL(jiffies_64);
struct timer_base {
raw_spinlock_t lock;
struct timer_list *running_timer;
+#ifdef CONFIG_PREEMPT_RT
+ spinlock_t expiry_lock;
+ atomic_t timer_waiters;
+#endif
unsigned long clk;
unsigned long next_expiry;
unsigned int cpu;
@@ -1227,7 +1231,78 @@ int try_to_del_timer_sync(struct timer_list *timer)
}
EXPORT_SYMBOL(try_to_del_timer_sync);
-#ifdef CONFIG_SMP
+#ifdef CONFIG_PREEMPT_RT
+static __init void timer_base_init_expiry_lock(struct timer_base *base)
+{
+ spin_lock_init(&base->expiry_lock);
+}
+
+static inline void timer_base_lock_expiry(struct timer_base *base)
+{
+ spin_lock(&base->expiry_lock);
+}
+
+static inline void timer_base_unlock_expiry(struct timer_base *base)
+{
+ spin_unlock(&base->expiry_lock);
+}
+
+/*
+ * The counterpart to del_timer_wait_running().
+ *
+ * If there is a waiter for base->expiry_lock, then it was waiting for the
+ * timer callback to finish. Drop expiry_lock and reaquire it. That allows
+ * the waiter to acquire the lock and make progress.
+ */
+static void timer_sync_wait_running(struct timer_base *base)
+{
+ if (atomic_read(&base->timer_waiters)) {
+ spin_unlock(&base->expiry_lock);
+ spin_lock(&base->expiry_lock);
+ }
+}
+
+/*
+ * This function is called on PREEMPT_RT kernels when the fast path
+ * deletion of a timer failed because the timer callback function was
+ * running.
+ *
+ * This prevents priority inversion, if the softirq thread on a remote CPU
+ * got preempted, and it prevents a life lock when the task which tries to
+ * delete a timer preempted the softirq thread running the timer callback
+ * function.
+ */
+static void del_timer_wait_running(struct timer_list *timer)
+{
+ u32 tf;
+
+ tf = READ_ONCE(timer->flags);
+ if (!(tf & TIMER_MIGRATING)) {
+ struct timer_base *base = get_timer_base(tf);
+
+ /*
+ * Mark the base as contended and grab the expiry lock,
+ * which is held by the softirq across the timer
+ * callback. Drop the lock immediately so the softirq can
+ * expire the next timer. In theory the timer could already
+ * be running again, but that's more than unlikely and just
+ * causes another wait loop.
+ */
+ atomic_inc(&base->timer_waiters);
+ spin_lock_bh(&base->expiry_lock);
+ atomic_dec(&base->timer_waiters);
+ spin_unlock_bh(&base->expiry_lock);
+ }
+}
+#else
+static inline void timer_base_init_expiry_lock(struct timer_base *base) { }
+static inline void timer_base_lock_expiry(struct timer_base *base) { }
+static inline void timer_base_unlock_expiry(struct timer_base *base) { }
+static inline void timer_sync_wait_running(struct timer_base *base) { }
+static inline void del_timer_wait_running(struct timer_list *timer) { }
+#endif
+
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
/**
* del_timer_sync - deactivate a timer and wait for the handler to finish.
* @timer: the timer to be deactivated
@@ -1266,6 +1341,8 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
*/
int del_timer_sync(struct timer_list *timer)
{
+ int ret;
+
#ifdef CONFIG_LOCKDEP
unsigned long flags;
@@ -1283,12 +1360,17 @@ int del_timer_sync(struct timer_list *timer)
* could lead to deadlock.
*/
WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
- for (;;) {
- int ret = try_to_del_timer_sync(timer);
- if (ret >= 0)
- return ret;
- cpu_relax();
- }
+
+ do {
+ ret = try_to_del_timer_sync(timer);
+
+ if (unlikely(ret < 0)) {
+ del_timer_wait_running(timer);
+ cpu_relax();
+ }
+ } while (ret < 0);
+
+ return ret;
}
EXPORT_SYMBOL(del_timer_sync);
#endif
@@ -1360,10 +1442,13 @@ static void expire_timers(struct timer_base *base, struct hlist_head *head)
if (timer->flags & TIMER_IRQSAFE) {
raw_spin_unlock(&base->lock);
call_timer_fn(timer, fn, baseclk);
+ base->running_timer = NULL;
raw_spin_lock(&base->lock);
} else {
raw_spin_unlock_irq(&base->lock);
call_timer_fn(timer, fn, baseclk);
+ base->running_timer = NULL;
+ timer_sync_wait_running(base);
raw_spin_lock_irq(&base->lock);
}
}
@@ -1658,6 +1743,7 @@ static inline void __run_timers(struct timer_base *base)
if (!time_after_eq(jiffies, base->clk))
return;
+ timer_base_lock_expiry(base);
raw_spin_lock_irq(&base->lock);
/*
@@ -1684,8 +1770,8 @@ static inline void __run_timers(struct timer_base *base)
while (levels--)
expire_timers(base, heads + levels);
}
- base->running_timer = NULL;
raw_spin_unlock_irq(&base->lock);
+ timer_base_unlock_expiry(base);
}
/*
@@ -1930,6 +2016,7 @@ static void __init init_timer_cpu(int cpu)
base->cpu = cpu;
raw_spin_lock_init(&base->lock);
base->clk = jiffies;
+ timer_base_init_expiry_lock(base);
}
}