[tip: timers/core] timers: Use del_timer_sync() even on UP

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     168f6b6ffbeec0b9333f3582e4cf637300858db5
Gitweb:        https://git.kernel.org/tip/168f6b6ffbeec0b9333f3582e4cf637300858db5
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Wed, 23 Nov 2022 21:18:42 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Thu, 24 Nov 2022 15:09:11 +01:00

timers: Use del_timer_sync() even on UP

del_timer_sync() is assumed to be pointless on uniprocessor systems and can
be mapped to del_timer() because in theory del_timer() can never be invoked
while the timer callback function is executed.

This is not entirely true because del_timer() can be invoked from interrupt
context and therefore hit in the middle of a running timer callback.

Contrary to that del_timer_sync() is not allowed to be invoked from
interrupt context unless the affected timer is marked with TIMER_IRQSAFE.
del_timer_sync() has proper checks in place to detect such a situation.

Give up on the UP optimization and make del_timer_sync() unconditionally
available.

Co-developed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
Reviewed-by: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20220407161745.7d6754b3@xxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20221110064101.429013735@xxxxxxxxxxx
Link: https://lore.kernel.org/r/20221123201624.888306160@xxxxxxxxxxxxx

---
 include/linux/timer.h | 7 +------
 kernel/time/timer.c   | 2 --
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/include/linux/timer.h b/include/linux/timer.h
index ea35d00..31b8b60 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -183,12 +183,7 @@ extern int timer_reduce(struct timer_list *timer, unsigned long expires);
 extern void add_timer(struct timer_list *timer);
 
 extern int try_to_del_timer_sync(struct timer_list *timer);
-
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
-  extern int del_timer_sync(struct timer_list *timer);
-#else
-# define del_timer_sync(t)		del_timer(t)
-#endif
+extern int del_timer_sync(struct timer_list *timer);
 
 extern void init_timers(void);
 struct hrtimer;
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ea0150c..550f0df 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1396,7 +1396,6 @@ static inline void timer_sync_wait_running(struct timer_base *base) { }
 static inline void del_timer_wait_running(struct timer_list *timer) { }
 #endif
 
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 /**
  * del_timer_sync - Deactivate a timer and wait for the handler to finish.
  * @timer:	The timer to be deactivated
@@ -1477,7 +1476,6 @@ int del_timer_sync(struct timer_list *timer)
 	return ret;
 }
 EXPORT_SYMBOL(del_timer_sync);
-#endif
 
 static void call_timer_fn(struct timer_list *timer,
 			  void (*fn)(struct timer_list *),