From 228a0950005c1da0600dd6333737110e7d701437 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 21 Jul 2011 15:23:39 +0200 Subject: [PATCH 131/278] 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 --- kernel/timer.c | 40 ++++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-) diff --git a/kernel/timer.c b/kernel/timer.c index d1bc5a9..8a9ca7d 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -654,6 +654,36 @@ 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) @@ -699,14 +729,8 @@ __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