timers: add mod_timer_pending()
Impact: new timer API
Based on an idea from Martin Josefsson with the help of
Patrick McHardy and Stephen Hemminger:
introduce the mod_timer_pending() API which is a mod_timer()
offspring that is an invariant on already removed timers.
(regular mod_timer() re-activates non-pending timers.)
This is useful for the networking code in that it can
allow unserialized mod_timer_pending() timer-forwarding
calls, but a single del_timer*() will stop the timer
from being reactivated again.
Also while at it:
- optimize the regular mod_timer() path some more, the
timer-stat and a debug check was needlessly duplicated
in __mod_timer().
- make the exports come straight after the function, as
most other exports in timer.c already did.
- eliminate __mod_timer() as an external API, change the
users to mod_timer().
The regular mod_timer() code path is not impacted
significantly, due to inlining optimizations and due to
the simplifications.
Based-on-patch-from: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Patrick McHardy <kaber@trash.net>
Cc: netdev@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/timer.c b/kernel/timer.c
index 13dd64f..9b77fc9 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -589,11 +589,14 @@
}
}
-int __mod_timer(struct timer_list *timer, unsigned long expires)
+static inline int
+__mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
{
struct tvec_base *base, *new_base;
unsigned long flags;
- int ret = 0;
+ int ret;
+
+ ret = 0;
timer_stats_timer_set_start_info(timer);
BUG_ON(!timer->function);
@@ -603,6 +606,9 @@
if (timer_pending(timer)) {
detach_timer(timer, 0);
ret = 1;
+ } else {
+ if (pending_only)
+ goto out_unlock;
}
debug_timer_activate(timer);
@@ -629,12 +635,83 @@
timer->expires = expires;
internal_add_timer(base, timer);
+
+out_unlock:
spin_unlock_irqrestore(&base->lock, flags);
return ret;
}
-EXPORT_SYMBOL(__mod_timer);
+/**
+ * mod_timer_pending - modify a pending timer's timeout
+ * @timer: the pending timer to be modified
+ * @expires: new timeout in jiffies
+ *
+ * mod_timer_pending() is the same for pending timers as mod_timer(),
+ * but will not re-activate and modify already deleted timers.
+ *
+ * It is useful for unserialized use of timers.
+ */
+int mod_timer_pending(struct timer_list *timer, unsigned long expires)
+{
+ return __mod_timer(timer, expires, true);
+}
+EXPORT_SYMBOL(mod_timer_pending);
+
+/**
+ * mod_timer - modify a timer's timeout
+ * @timer: the timer to be modified
+ * @expires: new timeout in jiffies
+ *
+ * mod_timer() is a more efficient way to update the expire field of an
+ * active timer (if the timer is inactive it will be activated)
+ *
+ * mod_timer(timer, expires) is equivalent to:
+ *
+ * del_timer(timer); timer->expires = expires; add_timer(timer);
+ *
+ * Note that if there are multiple unserialized concurrent users of the
+ * same timer, then mod_timer() is the only safe way to modify the timeout,
+ * since add_timer() cannot modify an already running timer.
+ *
+ * The function returns whether it has modified a pending timer or not.
+ * (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an
+ * active timer returns 1.)
+ */
+int mod_timer(struct timer_list *timer, unsigned long expires)
+{
+ /*
+ * This is a common optimization triggered by the
+ * networking code - if the timer is re-modified
+ * to be the same thing then just return:
+ */
+ if (timer->expires == expires && timer_pending(timer))
+ return 1;
+
+ return __mod_timer(timer, expires, false);
+}
+EXPORT_SYMBOL(mod_timer);
+
+/**
+ * add_timer - start a timer
+ * @timer: the timer to be added
+ *
+ * The kernel will do a ->function(->data) callback from the
+ * timer interrupt at the ->expires point in the future. The
+ * current time is 'jiffies'.
+ *
+ * The timer's ->expires, ->function (and if the handler uses it, ->data)
+ * fields must be set prior calling this function.
+ *
+ * Timers with an ->expires field in the past will be executed in the next
+ * timer tick.
+ */
+void add_timer(struct timer_list *timer)
+{
+ BUG_ON(timer_pending(timer));
+ mod_timer(timer, timer->expires);
+}
+EXPORT_SYMBOL(add_timer);
/**
* add_timer_on - start a timer on a particular CPU
@@ -667,44 +744,6 @@
}
/**
- * mod_timer - modify a timer's timeout
- * @timer: the timer to be modified
- * @expires: new timeout in jiffies
- *
- * mod_timer() is a more efficient way to update the expire field of an
- * active timer (if the timer is inactive it will be activated)
- *
- * mod_timer(timer, expires) is equivalent to:
- *
- * del_timer(timer); timer->expires = expires; add_timer(timer);
- *
- * Note that if there are multiple unserialized concurrent users of the
- * same timer, then mod_timer() is the only safe way to modify the timeout,
- * since add_timer() cannot modify an already running timer.
- *
- * The function returns whether it has modified a pending timer or not.
- * (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an
- * active timer returns 1.)
- */
-int mod_timer(struct timer_list *timer, unsigned long expires)
-{
- BUG_ON(!timer->function);
-
- timer_stats_timer_set_start_info(timer);
- /*
- * This is a common optimization triggered by the
- * networking code - if the timer is re-modified
- * to be the same thing then just return:
- */
- if (timer->expires == expires && timer_pending(timer))
- return 1;
-
- return __mod_timer(timer, expires);
-}
-
-EXPORT_SYMBOL(mod_timer);
-
-/**
* del_timer - deactive a timer.
* @timer: the timer to be deactivated
*
@@ -733,7 +772,6 @@
return ret;
}
-
EXPORT_SYMBOL(del_timer);
#ifdef CONFIG_SMP
@@ -767,7 +805,6 @@
return ret;
}
-
EXPORT_SYMBOL(try_to_del_timer_sync);
/**
@@ -796,7 +833,6 @@
cpu_relax();
}
}
-
EXPORT_SYMBOL(del_timer_sync);
#endif
@@ -1268,7 +1304,7 @@
expire = timeout + jiffies;
setup_timer_on_stack(&timer, process_timeout, (unsigned long)current);
- __mod_timer(&timer, expire);
+ __mod_timer(&timer, expire, false);
schedule();
del_singleshot_timer_sync(&timer);