From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 23 Nov 2022 21:18:50 +0100
Subject: timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown
mode
Patch-mainline: v6.2-rc1
Git-commit: 8553b5f2774a66b1f293b7d783934210afb8f23c
References: bsc#1213970
Tearing down timers which have circular dependencies to other
functionality, e.g. workqueues, where the timer can schedule work and work
can arm timers, is not trivial.
In those cases it is desired to shutdown the timer in a way which prevents
rearming of the timer. The mechanism to do so is to set timer->function to
NULL and use this as an indicator for the timer arming functions to ignore
the (re)arm request.
Split the inner workings of try_do_del_timer_sync(), del_timer_sync() and
del_timer() into helper functions to prepare for implementing the shutdown
functionality.
No functional change.
Co-developed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home
Link: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org
Link: https://lore.kernel.org/r/20221123201625.195147423@linutronix.de
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
kernel/time/timer.c | 137 +++++++++++++++++++++++++++++++++-------------------
1 file changed, 89 insertions(+), 48 deletions(-)
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1181,20 +1181,14 @@ out_unlock:
EXPORT_SYMBOL_GPL(add_timer_on);
/**
- * timer_delete - Deactivate a timer
+ * __timer_delete - Internal function: Deactivate a timer
* @timer: The timer to be deactivated
*
- * The function only deactivates a pending timer, but contrary to
- * timer_delete_sync() it does not take into account whether the timer's
- * callback function is concurrently executed on a different CPU or not.
- * It neither prevents rearming of the timer. If @timer can be rearmed
- * concurrently then the return value of this function is meaningless.
- *
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
*/
-int timer_delete(struct timer_list *timer)
+static int __timer_delete(struct timer_list *timer)
{
struct timer_base *base;
unsigned long flags;
@@ -1210,6 +1204,25 @@ int timer_delete(struct timer_list *time
return ret;
}
+
+/**
+ * timer_delete - Deactivate a timer
+ * @timer: The timer to be deactivated
+ *
+ * The function only deactivates a pending timer, but contrary to
+ * timer_delete_sync() it does not take into account whether the timer's
+ * callback function is concurrently executed on a different CPU or not.
+ * It neither prevents rearming of the timer. If @timer can be rearmed
+ * concurrently then the return value of this function is meaningless.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending and deactivated
+ */
+int timer_delete(struct timer_list *timer)
+{
+ return __timer_delete(timer);
+}
EXPORT_SYMBOL(timer_delete);
/**
@@ -1222,27 +1235,20 @@ EXPORT_SYMBOL(timer_delete);
*/
int del_timer(struct timer_list *timer)
{
- return timer_delete(timer);
+ return __timer_delete(timer);
}
EXPORT_SYMBOL(del_timer);
/**
- * try_to_del_timer_sync - Try to deactivate a timer
+ * __try_to_del_timer_sync - Internal function: Try to deactivate a timer
* @timer: Timer to deactivate
*
- * This function tries to deactivate a timer. On success the timer is not
- * queued and the timer callback function is not running on any CPU.
- *
- * This function does not guarantee that the timer cannot be rearmed right
- * after dropping the base lock. That needs to be prevented by the calling
- * code if necessary.
- *
* Return:
* * %0 - The timer was not pending
* * %1 - The timer was pending and deactivated
* * %-1 - The timer callback function is running on a different CPU
*/
-int try_to_del_timer_sync(struct timer_list *timer)
+static int __try_to_del_timer_sync(struct timer_list *timer)
{
struct timer_base *base;
unsigned long flags;
@@ -1259,9 +1265,66 @@ int try_to_del_timer_sync(struct timer_l
return ret;
}
+
+/**
+ * try_to_del_timer_sync - Try to deactivate a timer
+ * @timer: Timer to deactivate
+ *
+ * This function tries to deactivate a timer. On success the timer is not
+ * queued and the timer callback function is not running on any CPU.
+ *
+ * This function does not guarantee that the timer cannot be rearmed right
+ * after dropping the base lock. That needs to be prevented by the calling
+ * code if necessary.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending and deactivated
+ * * %-1 - The timer callback function is running on a different CPU
+ */
+int try_to_del_timer_sync(struct timer_list *timer)
+{
+ return __try_to_del_timer_sync(timer);
+}
EXPORT_SYMBOL(try_to_del_timer_sync);
/**
+ * __timer_delete_sync - Internal function: Deactivate a timer and wait
+ * for the handler to finish.
+ * @timer: The timer to be deactivated
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending and deactivated
+ */
+static int __timer_delete_sync(struct timer_list *timer)
+{
+#ifdef CONFIG_LOCKDEP
+ unsigned long flags;
+
+ /*
+ * If lockdep gives a backtrace here, please reference
+ * the synchronization rules above.
+ */
+ local_irq_save(flags);
+ lock_map_acquire(&timer->lockdep_map);
+ lock_map_release(&timer->lockdep_map);
+ local_irq_restore(flags);
+#endif
+ /*
+ * don't use it in hardirq context, because it
+ * could lead to deadlock.
+ */
+ WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
+ for (;;) {
+ int ret = __try_to_del_timer_sync(timer);
+ if (ret >= 0)
+ return ret;
+ cpu_relax();
+ }
+}
+
+/**
* timer_delete_sync - Deactivate a timer and wait for the handler to finish.
* @timer: The timer to be deactivated
*
@@ -1278,14 +1341,14 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
*
* CPU0 CPU1
* ---- ----
- * <SOFTIRQ>
- * call_timer_fn();
- * base->running_timer = mytimer;
- * spin_lock_irq(somelock);
+ * <SOFTIRQ>
+ * call_timer_fn();
+ * base->running_timer = mytimer;
+ * spin_lock_irq(somelock);
* <IRQ>
* spin_lock(somelock);
- * del_timer_sync(mytimer);
- * while (base->running_timer == mytimer);
+ * timer_delete_sync(mytimer);
+ * while (base->running_timer == mytimer);
*
* Now timer_delete_sync() will never return and never release somelock.
* The interrupt on the other CPU is waiting to grab somelock but it has
@@ -1302,29 +1365,7 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
*/
int timer_delete_sync(struct timer_list *timer)
{
-#ifdef CONFIG_LOCKDEP
- unsigned long flags;
-
- /*
- * If lockdep gives a backtrace here, please reference
- * the synchronization rules above.
- */
- local_irq_save(flags);
- lock_map_acquire(&timer->lockdep_map);
- lock_map_release(&timer->lockdep_map);
- local_irq_restore(flags);
-#endif
- /*
- * don't use it in hardirq context, because it
- * could lead to deadlock.
- */
- WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
- for (;;) {
- int ret = try_to_del_timer_sync(timer);
- if (ret >= 0)
- return ret;
- cpu_relax();
- }
+ return __timer_delete_sync(timer);
}
EXPORT_SYMBOL(timer_delete_sync);
@@ -1338,7 +1379,7 @@ EXPORT_SYMBOL(timer_delete_sync);
*/
int del_timer_sync(struct timer_list *timer)
{
- return timer_delete_sync(timer);
+ return __timer_delete_sync(timer);
}
EXPORT_SYMBOL(del_timer_sync);