75 lines
2.2 KiB
Diff
75 lines
2.2 KiB
Diff
Subject: timers: Avoid the switch timers base set to NULL trick on RT
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Thu, 21 Jul 2011 15:23:39 +0200
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz
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On RT that code is preemptible, so we cannot assign NULL to timers
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base as a preempter would spin forever in lock_timer_base().
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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kernel/time/timer.c | 45 +++++++++++++++++++++++++++++++++++----------
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1 file changed, 35 insertions(+), 10 deletions(-)
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--- a/kernel/time/timer.c
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+++ b/kernel/time/timer.c
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@@ -780,6 +780,39 @@ static struct tvec_base *lock_timer_base
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cpu_relax();
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}
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}
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+static inline struct tvec_base *switch_timer_base(struct timer_list *timer,
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+ struct tvec_base *old,
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+ struct tvec_base *new)
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+{
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+ /*
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+ * We cannot do the below because we might be preempted and
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+ * then the preempter would see NULL and loop forever.
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+ */
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+ if (spin_trylock(&new->lock)) {
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+ WRITE_ONCE(timer->flags,
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+ (timer->flags & ~TIMER_BASEMASK) | new->cpu);
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+ spin_unlock(&old->lock);
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+ return new;
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+ }
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+ return old;
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+}
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+
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+#else
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+static inline struct tvec_base *switch_timer_base(struct timer_list *timer,
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+ struct tvec_base *old,
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+ struct tvec_base *new)
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+{
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+ /* See the comment in lock_timer_base() */
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+ timer->flags |= TIMER_MIGRATING;
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+
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+ spin_unlock(&old->lock);
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+ spin_lock(&new->lock);
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+ WRITE_ONCE(timer->flags,
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+ (timer->flags & ~TIMER_BASEMASK) | new->cpu);
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+ return new;
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+}
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+#endif
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static inline int
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__mod_timer(struct timer_list *timer, unsigned long expires,
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@@ -810,16 +843,8 @@ static inline int
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* handler yet has not finished. This also guarantees that
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* the timer is serialized wrt itself.
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*/
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- if (likely(base->running_timer != timer)) {
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- /* See the comment in lock_timer_base() */
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- timer->flags |= TIMER_MIGRATING;
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-
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- spin_unlock(&base->lock);
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- base = new_base;
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- spin_lock(&base->lock);
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- WRITE_ONCE(timer->flags,
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- (timer->flags & ~TIMER_BASEMASK) | base->cpu);
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- }
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+ if (likely(base->running_timer != timer))
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+ base = switch_timer_base(timer, base, new_base);
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}
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timer->expires = expires;
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