[PATCH 5.4 005/215] timers: Use del_timer_sync() even on UP

Greg Kroah-Hartman
2024-04-11T10:15:10Z

From: Thomas Gleixner <tglx@linutronix.de>

[ Upstream commit 168f6b6ffbeec0b9333f3582e4cf637300858db5 ]

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@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/20221123201624.888306160@linutronix.de
Stable-dep-of: 0f7352557a35 ("wifi: brcmfmac: Fix use-after-free bug in brcmf_cfg80211_detach")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 1e6650ed066d5..4de865f516154 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -182,12 +182,7 @@ 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);

#define del_singleshot_timer_sync(t) del_timer_sync(t)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 973c66d9b3f90..0dfd1cacc4a00 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1345,7 +1345,6 @@ 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
@@ -1419,7 +1418,6 @@ 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 *),
--
2.43.0