Commit 3bb475a3 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

timers: Sanitize catchup_timer_jiffies() usage 



catchup_timer_jiffies() has been applied blindly to several functions
without looking for possible better ways to do it.

1) internal_add_timer()

   Move the update to base->all_timers before we actually insert the
   timer into the wheel.

2) detach_if_pending()

   Again the update to base->all_timers allows us to explicitely do
   the timer_jiffies update in place, if this was the last timer which
   got removed.

3) __run_timers()

   We only check on entry, which is silly, because base->timer_jiffies
   can be behind - especially on NOHZ kernels - and if there is a
   single deferrable timer somewhere between base->timer_jiffies and
   jiffies we expire it and then loop until base->timer_jiffies ==
   jiffies.

   Move it into the loop.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Joonwoo Park <joonwoop@codeaurora.org>
Cc: Wenbo Wang <wenbo.wang@memblaze.com>
Link: http://lkml.kernel.org/r/20150526224511.662994644@linutronix.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 887d9dc9

kernel/time/timer.c

+16 −24
Original line number Diff line number Diff line
@@ -351,20 +351,6 @@ void set_timer_slack(struct timer_list *timer, int slack_hz) 
}

EXPORT_SYMBOL_GPL(set_timer_slack);



/*

 * If the list is empty, catch up ->timer_jiffies to the current time.

 * The caller must hold the tvec_base lock.  Returns true if the list

 * was empty and therefore ->timer_jiffies was updated.

 */

static bool catchup_timer_jiffies(struct tvec_base *base)

{

	if (!base->all_timers) {

		base->timer_jiffies = jiffies;

		return true;

	}

	return false;

}



static void

__internal_add_timer(struct tvec_base *base, struct timer_list *timer)

{
@@ -411,7 +397,10 @@ __internal_add_timer(struct tvec_base *base, struct timer_list *timer) 


static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)

{

	(void)catchup_timer_jiffies(base);

	/* Advance base->jiffies, if the base is empty */

	if (!base->all_timers++)

		base->timer_jiffies = jiffies;



	__internal_add_timer(base, timer);

	/*

	 * Update base->active_timers and base->next_timer
@@ -421,7 +410,6 @@ static void internal_add_timer(struct tvec_base *base, struct timer_list *timer) 
		    time_before(timer->expires, base->next_timer))

			base->next_timer = timer->expires;

	}

	base->all_timers++;



	/*

	 * Check whether the other CPU is in dynticks mode and needs
@@ -718,7 +706,6 @@ detach_expired_timer(struct timer_list *timer, struct tvec_base *base) 
	if (!tbase_get_deferrable(timer->base))

		base->active_timers--;

	base->all_timers--;

	(void)catchup_timer_jiffies(base);

}



static int detach_if_pending(struct timer_list *timer, struct tvec_base *base,
@@ -733,8 +720,9 @@ static int detach_if_pending(struct timer_list *timer, struct tvec_base *base, 
		if (timer->expires == base->next_timer)

			base->next_timer = base->timer_jiffies;

	}

	base->all_timers--;

	(void)catchup_timer_jiffies(base);

	/* If this was the last timer, advance base->jiffies */

	if (!--base->all_timers)

		base->timer_jiffies = jiffies;

	return 1;

}
@@ -1184,14 +1172,18 @@ static inline void __run_timers(struct tvec_base *base) 
	struct timer_list *timer;



	spin_lock_irq(&base->lock);

	if (catchup_timer_jiffies(base)) {

		spin_unlock_irq(&base->lock);

		return;

	}



	while (time_after_eq(jiffies, base->timer_jiffies)) {

		struct list_head work_list;

		struct list_head *head = &work_list;

		int index = base->timer_jiffies & TVR_MASK;

		int index;



		if (!base->all_timers) {

			base->timer_jiffies = jiffies;

			break;

		}



		index = base->timer_jiffies & TVR_MASK;



		/*

		 * Cascade timers:

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