From dd6414b50fa2b1cd247a8aa8f8bd42414b7453e1 Mon Sep 17 00:00:00 2001 From: Phil Carmody Date: Wed, 20 Oct 2010 15:57:33 -0700 Subject: timer: Permit statically-declared work with deferrable timers Currently, you have to just define a delayed_work uninitialised, and then initialise it before first use. That's a tad clumsy. At risk of playing mind-games with the compiler, fooling it into doing pointer arithmetic with compile-time-constants, this lets clients properly initialise delayed work with deferrable timers statically. This patch was inspired by the issues which lead Artem Bityutskiy to commit 8eab945c5616fc984 ("sunrpc: make the cache cleaner workqueue deferrable"). Signed-off-by: Phil Carmody Acked-by: Artem Bityutskiy Cc: Arjan van de Ven Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/timer.c | 15 +-------------- 1 file changed, 1 insertion(+), 14 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 97bf05b..72853b2 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -88,18 +88,6 @@ struct tvec_base boot_tvec_bases; EXPORT_SYMBOL(boot_tvec_bases); static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases; -/* - * Note that all tvec_bases are 2 byte aligned and lower bit of - * base in timer_list is guaranteed to be zero. Use the LSB to - * indicate whether the timer is deferrable. - * - * A deferrable timer will work normally when the system is busy, but - * will not cause a CPU to come out of idle just to service it; instead, - * the timer will be serviced when the CPU eventually wakes up with a - * subsequent non-deferrable timer. - */ -#define TBASE_DEFERRABLE_FLAG (0x1) - /* Functions below help us manage 'deferrable' flag */ static inline unsigned int tbase_get_deferrable(struct tvec_base *base) { @@ -113,8 +101,7 @@ static inline struct tvec_base *tbase_get_base(struct tvec_base *base) static inline void timer_set_deferrable(struct timer_list *timer) { - timer->base = ((struct tvec_base *)((unsigned long)(timer->base) | - TBASE_DEFERRABLE_FLAG)); + timer->base = TBASE_MAKE_DEFERRED(timer->base); } static inline void -- cgit v1.1 From 6f1bc451e6a79470b122a37ee1fc6bbca450f444 Mon Sep 17 00:00:00 2001 From: Yong Zhang Date: Wed, 20 Oct 2010 15:57:31 -0700 Subject: timer: Make try_to_del_timer_sync() the same on SMP and UP On UP try_to_del_timer_sync() is mapped to del_timer() which does not take the running timer callback into account, so it has different semantics. Remove the SMP dependency of try_to_del_timer_sync() by using base->running_timer in the UP case as well. [ tglx: Removed set_running_timer() inline and tweaked the changelog ] Signed-off-by: Yong Zhang Cc: Ingo Molnar Cc: Peter Zijlstra Acked-by: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/timer.c | 17 +++-------------- 1 file changed, 3 insertions(+), 14 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 72853b2..47b86c1 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -330,15 +330,6 @@ void set_timer_slack(struct timer_list *timer, int slack_hz) } EXPORT_SYMBOL_GPL(set_timer_slack); - -static inline void set_running_timer(struct tvec_base *base, - struct timer_list *timer) -{ -#ifdef CONFIG_SMP - base->running_timer = timer; -#endif -} - static void internal_add_timer(struct tvec_base *base, struct timer_list *timer) { unsigned long expires = timer->expires; @@ -923,15 +914,12 @@ int del_timer(struct timer_list *timer) } EXPORT_SYMBOL(del_timer); -#ifdef CONFIG_SMP /** * try_to_del_timer_sync - Try to deactivate a timer * @timer: timer do del * * This function tries to deactivate a timer. Upon successful (ret >= 0) * exit the timer is not queued and the handler is not running on any CPU. - * - * It must not be called from interrupt contexts. */ int try_to_del_timer_sync(struct timer_list *timer) { @@ -960,6 +948,7 @@ out: } EXPORT_SYMBOL(try_to_del_timer_sync); +#ifdef CONFIG_SMP /** * del_timer_sync - deactivate a timer and wait for the handler to finish. * @timer: the timer to be deactivated @@ -1098,7 +1087,7 @@ static inline void __run_timers(struct tvec_base *base) timer_stats_account_timer(timer); - set_running_timer(base, timer); + base->running_timer = timer; detach_timer(timer, 1); spin_unlock_irq(&base->lock); @@ -1106,7 +1095,7 @@ static inline void __run_timers(struct tvec_base *base) spin_lock_irq(&base->lock); } } - set_running_timer(base, NULL); + base->running_timer = NULL; spin_unlock_irq(&base->lock); } -- cgit v1.1 From 1118e2cd33d47254854e1ba3ba8e32802ff14fdf Mon Sep 17 00:00:00 2001 From: Yong Zhang Date: Wed, 20 Oct 2010 15:57:32 -0700 Subject: timer: Del_timer_sync() can be used in softirq context Actually we have used del_timer_sync() in softirq context for a long time, e.g. in __dst_free()::cancel_delayed_work(). So change the comments of it to warn on hardirq context only, and make lockdep know about this change. Signed-off-by: Yong Zhang Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/timer.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 47b86c1..612de03 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -959,7 +959,7 @@ EXPORT_SYMBOL(try_to_del_timer_sync); * * Synchronization rules: Callers must prevent restarting of the timer, * otherwise this function is meaningless. It must not be called from - * interrupt contexts. The caller must not hold locks which would prevent + * hardirq contexts. The caller must not hold locks which would prevent * completion of the timer's handler. The timer's handler must not call * add_timer_on(). Upon exit the timer is not queued and the handler is * not running on any CPU. @@ -969,12 +969,10 @@ EXPORT_SYMBOL(try_to_del_timer_sync); int del_timer_sync(struct timer_list *timer) { #ifdef CONFIG_LOCKDEP - unsigned long flags; - - local_irq_save(flags); + local_bh_disable(); lock_map_acquire(&timer->lockdep_map); lock_map_release(&timer->lockdep_map); - local_irq_restore(flags); + local_bh_enable(); #endif for (;;) { -- cgit v1.1 From 466bd3030973910118ca601da8072be97a1e2209 Mon Sep 17 00:00:00 2001 From: Yong Zhang Date: Wed, 20 Oct 2010 15:57:33 -0700 Subject: timer: Warn when del_timer_sync() is called in hardirq context Add explict warning when del_timer_sync() is called in hardirq context. Signed-off-by: Yong Zhang Cc: Ingo Molnar Cc: Peter Zijlstra Acked-by: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner --- kernel/timer.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 612de03..483e54b 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -974,7 +974,11 @@ int del_timer_sync(struct timer_list *timer) lock_map_release(&timer->lockdep_map); local_bh_enable(); #endif - + /* + * don't use it in hardirq context, because it + * could lead to deadlock. + */ + WARN_ON(in_irq()); for (;;) { int ret = try_to_del_timer_sync(timer); if (ret >= 0) -- cgit v1.1 From 7496351ad87e61e96b49dd7b43c6534e3401f566 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Tue, 30 Nov 2010 14:05:53 -0600 Subject: timers: Use this_cpu_read Eric asked for this. [tglx: Because it generates faster code according to Erics ] Signed-off-by: Christoph Lameter Cc: Pekka Enberg Cc: Eric Dumazet Cc: Mathieu Desnoyers Cc: Tejun Heo Cc: linux-mm@kvack.org LKML-Reference: Signed-off-by: Thomas Gleixner --- kernel/timer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 483e54b..beb97fd 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1227,7 +1227,7 @@ static unsigned long cmp_next_hrtimer_event(unsigned long now, */ unsigned long get_next_timer_interrupt(unsigned long now) { - struct tvec_base *base = __get_cpu_var(tvec_bases); + struct tvec_base *base = __this_cpu_read(tvec_bases); unsigned long expires; spin_lock(&base->lock); @@ -1267,7 +1267,7 @@ void update_process_times(int user_tick) */ static void run_timer_softirq(struct softirq_action *h) { - struct tvec_base *base = __get_cpu_var(tvec_bases); + struct tvec_base *base = __this_cpu_read(tvec_bases); hrtimer_run_pending(); -- cgit v1.1