[RFC][PATCH 2/2] time: alarmtimer: Use TASK_FREEZABLE to cleanup freezer handling

[John Stultz <jstultz@google.com>]

Instead of trying to handle the freezer waking up tasks from
schedule() in nanosleep on alarmtimers explicitly, use
TASK_FREEZABLE which marks the task freezable when it goes
to schedule, which prevents the signal wakeup.

This allows for the freezer handling to be removed, simplifying
the code.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michael <michael@mipisi.de>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Cc: kernel-team@android.com
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/alpine.DEB.2.21.1909021247250.3955@nanos.tec.linutronix.de/
[jstultz: Forward ported to 6.2-rc and split out from a separate
          fix.]
Signed-off-by: John Stultz <jstultz@google.com>
---
 kernel/time/alarmtimer.c | 53 ++--------------------------------------
 1 file changed, 2 insertions(+), 51 deletions(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index f7b2128f64e2..15ecde8fcc1b 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -49,14 +49,6 @@ static struct alarm_base {
 	clockid_t		base_clockid;
 } alarm_bases[ALARM_NUMTYPE];
 
-#if defined(CONFIG_POSIX_TIMERS) || defined(CONFIG_RTC_CLASS)
-/* freezer information to handle clock_nanosleep triggered wakeups */
-static enum alarmtimer_type freezer_alarmtype;
-static ktime_t freezer_expires;
-static ktime_t freezer_delta;
-static DEFINE_SPINLOCK(freezer_delta_lock);
-#endif
-
 #ifdef CONFIG_RTC_CLASS
 /* rtc timer and device for setting alarm wakeups at suspend */
 static struct rtc_timer		rtctimer;
@@ -241,19 +233,12 @@ EXPORT_SYMBOL_GPL(alarm_expires_remaining);
  */
 static int alarmtimer_suspend(struct device *dev)
 {
-	ktime_t min, now, expires;
+	ktime_t now, expires, min = KTIME_MAX;
 	int i, ret, type;
 	struct rtc_device *rtc;
 	unsigned long flags;
 	struct rtc_time tm;
 
-	spin_lock_irqsave(&freezer_delta_lock, flags);
-	min = freezer_delta;
-	expires = freezer_expires;
-	type = freezer_alarmtype;
-	freezer_delta = KTIME_MAX;
-	spin_unlock_irqrestore(&freezer_delta_lock, flags);
-
 	rtc = alarmtimer_get_rtcdev();
 	/* If we have no rtcdev, just return */
 	if (!rtc)
@@ -480,38 +465,6 @@ u64 alarm_forward_now(struct alarm *alarm, ktime_t interval)
 EXPORT_SYMBOL_GPL(alarm_forward_now);
 
 #ifdef CONFIG_POSIX_TIMERS
-
-static void alarmtimer_freezerset(ktime_t absexp, enum alarmtimer_type type)
-{
-	struct alarm_base *base;
-	unsigned long flags;
-	ktime_t delta;
-
-	switch(type) {
-	case ALARM_REALTIME:
-		base = &alarm_bases[ALARM_REALTIME];
-		type = ALARM_REALTIME_FREEZER;
-		break;
-	case ALARM_BOOTTIME:
-		base = &alarm_bases[ALARM_BOOTTIME];
-		type = ALARM_BOOTTIME_FREEZER;
-		break;
-	default:
-		WARN_ONCE(1, "Invalid alarm type: %d\n", type);
-		return;
-	}
-
-	delta = ktime_sub(absexp, base->get_ktime());
-
-	spin_lock_irqsave(&freezer_delta_lock, flags);
-	if (delta < freezer_delta) {
-		freezer_delta = delta;
-		freezer_expires = absexp;
-		freezer_alarmtype = type;
-	}
-	spin_unlock_irqrestore(&freezer_delta_lock, flags);
-}
-
 /**
  * clock2alarm - helper that converts from clockid to alarmtypes
  * @clockid: clockid.
@@ -750,7 +703,7 @@ static int alarmtimer_do_nsleep(struct alarm *alarm, ktime_t absexp,
 	struct restart_block *restart;
 	alarm->data = (void *)current;
 	do {
-		set_current_state(TASK_INTERRUPTIBLE);
+		set_current_state(TASK_INTERRUPTIBLE | TASK_FREEZABLE);
 		alarm_start(alarm, absexp);
 		if (likely(alarm->data))
 			schedule();
@@ -765,8 +718,6 @@ static int alarmtimer_do_nsleep(struct alarm *alarm, ktime_t absexp,
 	if (!alarm->data)
 		return 0;
 
-	if (freezing(current))
-		alarmtimer_freezerset(absexp, type);
 	restart = &current->restart_block;
 	if (restart->nanosleep.type != TT_NONE) {
 		struct timespec64 rmt;
-- 
2.39.1.581.gbfd45094c4-goog