New rules:
->_base & 1 : is timer pending
->_base & ~1 : where the timer was last scheduled
->_base == NULL means that this timer is not running on any cpu.
del_timer_sync() clears ->_base, it is merely an optimization, so
that subsequent del_timer calls do not need locking.
del_timer_sync() assumes that the timer's base == (->_base & ~1)
can't be changed during execution of timer->function. It is achieved
by the next patch.
Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
--- 2.6.12-rc1/include/linux/timer.h~2_SYNC 2005-03-19 15:05:46.000000000
+0300
+++ 2.6.12-rc1/include/linux/timer.h 2005-03-19 15:28:13.000000000 +0300
@@ -21,9 +21,26 @@ struct timer_list {
struct tvec_t_base_s *_base;
};
+/*
+ * To save space, we play games with the least significant bit
+ * of timer_list->_base.
+ *
+ * If (_base & __TIMER_PENDING), the timer is pending. Implies
+ * (_base & ~__TIMER_PENDING) != NULL.
+ *
+ * (_base & ~__TIMER_PENDING), if != NULL, is the address of the
+ * timer's per-cpu tvec_t_base_s where it was last scheduled and
+ * where it may still be running.
+ *
+ * If (_base == NULL), the timer was not scheduled yet or it was
+ * cancelled by del_timer_sync(), so it is not running on any CPU.
+ */
+
+#define __TIMER_PENDING 1
+
static inline int __timer_pending(struct tvec_t_base_s *base)
{
- return base != NULL;
+ return ((unsigned long)base & __TIMER_PENDING) != 0;
}
#define TIMER_MAGIC 0x4b87ad6e
--- 2.6.12-rc1/kernel/timer.c~2_SYNC 2005-03-19 15:05:46.000000000 +0300
+++ 2.6.12-rc1/kernel/timer.c 2005-03-19 17:19:44.000000000 +0300
@@ -88,16 +88,26 @@ static inline void set_running_timer(tve
static inline tvec_base_t *__get_base(struct timer_list *timer)
{
- return timer->_base;
+ tvec_base_t *base = timer->_base;
+
+ if (__timer_pending(base))
+ return (void*)base - __TIMER_PENDING;
+ else
+ return NULL;
}
static inline void __set_base(struct timer_list *timer,
tvec_base_t *base, int pending)
{
if (pending)
- timer->_base = base;
+ timer->_base = (void*)base + __TIMER_PENDING;
else
- timer->_base = NULL;
+ timer->_base = base;
+}
+
+static inline tvec_base_t *timer_base(struct timer_list *timer)
+{
+ return (tvec_base_t*)((unsigned long)timer->_base & ~__TIMER_PENDING);
}
/* Fake initialization */
@@ -346,41 +356,46 @@ EXPORT_SYMBOL(del_timer);
* 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
- * completion of the timer's handler. Upon exit the timer is not queued and
- * the handler is not running on any CPU.
+ * 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.
*
* The function returns whether it has deactivated a pending timer or not.
- *
- * del_timer_sync() is slow and complicated because it copes with timer
- * handlers which re-arm the timer (periodic timers). If the timer handler
- * is known to not do this (a single shot timer) then use
- * del_singleshot_timer_sync() instead.
*/
int del_timer_sync(struct timer_list *timer)
{
- tvec_base_t *base;
- int i, ret = 0;
+ int ret;
check_timer(timer);
-del_again:
- ret += del_timer(timer);
+ ret = 0;
+ for (;;) {
+ unsigned long flags;
+ tvec_base_t *base;
- for_each_online_cpu(i) {
- base = &per_cpu(tvec_bases, i);
- if (base->running_timer == timer) {
- while (base->running_timer == timer) {
- cpu_relax();
- preempt_check_resched();
- }
- break;
+ base = timer_base(timer);
+ if (!base)
+ return ret;
+
+ spin_lock_irqsave(&base->lock, flags);
+
+ if (base->running_timer == timer)
+ goto unlock;
+
+ if (timer_base(timer) != base)
+ goto unlock;
+
+ if (timer_pending(timer)) {
+ list_del(&timer->entry);
+ ret = 1;
}
+ /* Need to make sure that anybody who sees a NULL base
+ * also sees the list ops */
+ smp_wmb();
+ timer->_base = NULL;
+unlock:
+ spin_unlock_irqrestore(&base->lock, flags);
}
- smp_rmb();
- if (timer_pending(timer))
- goto del_again;
-
- return ret;
}
EXPORT_SYMBOL(del_timer_sync);
-
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