David Mosberger <davidm@napali.hpl.hp.com> wrote:
>
> It appears to me that this changeset:
>
> http://linux.bkbits.net:8080/linux-2.5/diffs/kernel/timer.c@1.48
>
> may have gone a little too far.
>
> What I'm seeing is that if someone happens to arm a periodic timer at
> exactly 256 jiffies (as ohci happens to do on platforms with HZ=1024),
> then you end up getting an endless loop of timer activations, causing
> a machine hang.
>
> The problem is that __run_timers updates base->timer_jiffies _before_
> running the callback routines. If a callback re-arms the timer at
> exactly 256 jiffies, add_timers() will reinsert the timer into the
> list that we're currently processing, which of course will cause the
> timer to expire immediately again, etc., etc., ad naseum...
>
OK, well unless George can pull a rabbit out of the hat it may
be best to just revert it.
This gives us the same algorithm as 2.4, which I think is good.
--- 25/kernel/timer.c~timer-simplification-revert 2003-04-11 00:19:48.000000000 -0700
+++ 25-akpm/kernel/timer.c 2003-04-11 00:19:48.000000000 -0700
@@ -56,6 +56,7 @@ struct tvec_t_base_s {
spinlock_t lock;
unsigned long timer_jiffies;
struct timer_list *running_timer;
+ struct list_head *run_timer_list_running;
tvec_root_t tv1;
tvec_t tv2;
tvec_t tv3;
@@ -100,6 +101,12 @@ static inline void check_timer(struct ti
check_timer_failed(timer);
}
+/*
+ * If a timer handler re-adds the timer with expires == jiffies, the timer
+ * running code can lock up. So here we detect that situation and park the
+ * timer onto base->run_timer_list_running. It will be added to the main timer
+ * structures later, by __run_timers().
+ */
static void internal_add_timer(tvec_base_t *base, struct timer_list *timer)
{
@@ -107,7 +114,9 @@ static void internal_add_timer(tvec_base
unsigned long idx = expires - base->timer_jiffies;
struct list_head *vec;
- if (idx < TVR_SIZE) {
+ if (base->run_timer_list_running) {
+ vec = base->run_timer_list_running;
+ } else if (idx < TVR_SIZE) {
int i = expires & TVR_MASK;
vec = base->tv1.vec + i;
} else if (idx < 1 << (TVR_BITS + TVN_BITS)) {
@@ -397,6 +406,7 @@ static inline void __run_timers(tvec_bas
spin_lock_irq(&base->lock);
while (time_after_eq(jiffies, base->timer_jiffies)) {
+ LIST_HEAD(deferred_timers);
struct list_head *head;
int index = base->timer_jiffies & TVR_MASK;
@@ -408,7 +418,7 @@ static inline void __run_timers(tvec_bas
(!cascade(base, &base->tv3, INDEX(1))) &&
!cascade(base, &base->tv4, INDEX(2)))
cascade(base, &base->tv5, INDEX(3));
- ++base->timer_jiffies;
+ base->run_timer_list_running = &deferred_timers;
repeat:
head = base->tv1.vec + index;
if (!list_empty(head)) {
@@ -427,6 +437,14 @@ repeat:
spin_lock_irq(&base->lock);
goto repeat;
}
+ base->run_timer_list_running = NULL;
+ ++base->timer_jiffies;
+ while (!list_empty(&deferred_timers)) {
+ timer = list_entry(deferred_timers.prev,
+ struct timer_list, entry);
+ list_del(&timer->entry);
+ internal_add_timer(base, timer);
+ }
}
set_running_timer(base, NULL);
spin_unlock_irq(&base->lock);
_
-
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This archive was generated by hypermail 2b29 : Tue Apr 15 2003 - 22:00:22 EST