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From 51ecb820a14beb84d7ea503cb004883b29775e9e Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 21 Jul 2011 15:23:39 +0200
Subject: [PATCH 113/274] timers: Avoid the switch timers base set to NULL
trick on RT
On RT that code is preemptible, so we cannot assign NULL to timers
base as a preempter would spin forever in lock_timer_base().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/timer.c | 40 ++++++++++++++++++++++++++++++++--------
1 file changed, 32 insertions(+), 8 deletions(-)
diff --git a/kernel/timer.c b/kernel/timer.c
index 4dbfeb6..2342d25 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -702,6 +702,36 @@ static struct tvec_base *lock_timer_base(struct timer_list *timer,
}
}
+#ifndef CONFIG_PREEMPT_RT_FULL
+static inline struct tvec_base *switch_timer_base(struct timer_list *timer,
+ struct tvec_base *old,
+ struct tvec_base *new)
+{
+ /* See the comment in lock_timer_base() */
+ timer_set_base(timer, NULL);
+ spin_unlock(&old->lock);
+ spin_lock(&new->lock);
+ timer_set_base(timer, new);
+ return new;
+}
+#else
+static inline struct tvec_base *switch_timer_base(struct timer_list *timer,
+ struct tvec_base *old,
+ struct tvec_base *new)
+{
+ /*
+ * We cannot do the above because we might be preempted and
+ * then the preempter would see NULL and loop forever.
+ */
+ if (spin_trylock(&new->lock)) {
+ timer_set_base(timer, new);
+ spin_unlock(&old->lock);
+ return new;
+ }
+ return old;
+}
+#endif
+
static inline int
__mod_timer(struct timer_list *timer, unsigned long expires,
bool pending_only, int pinned)
@@ -747,14 +777,8 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
* handler yet has not finished. This also guarantees that
* the timer is serialized wrt itself.
*/
- if (likely(base->running_timer != timer)) {
- /* See the comment in lock_timer_base() */
- timer_set_base(timer, NULL);
- spin_unlock(&base->lock);
- base = new_base;
- spin_lock(&base->lock);
- timer_set_base(timer, base);
- }
+ if (likely(base->running_timer != timer))
+ base = switch_timer_base(timer, base, new_base);
}
timer->expires = expires;
--
1.7.10.4
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