linux-kernel - [PATCH v1 1/2] rtc: add lockless rtc_update_irq

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Date:   Wed, 9 Nov 2022 14:41:46 +0800
From:   Yu Liao <liaoyu15@...wei.com>
To:     <alexandre.belloni@...tlin.com>, <a.zummo@...ertech.it>
CC:     <liaoyu15@...wei.com>, <liwei391@...wei.com>,
        <linux-kernel@...r.kernel.org>, <linux-rtc@...r.kernel.org>
Subject: [PATCH v1 1/2] rtc: add lockless rtc_update_irq_enable

Split out a function that does not acquire rtc->ops_lock from
rtc_update_irq_enable, in preparation for fixing race condition in
rtc_set_time.

Signed-off-by: Yu Liao <liaoyu15@...wei.com>
---
 drivers/rtc/interface.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 9edd662c69ac..bc55dd31bece 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -19,6 +19,7 @@
 
 static int rtc_timer_enqueue(struct rtc_device *rtc, struct rtc_timer *timer);
 static void rtc_timer_remove(struct rtc_device *rtc, struct rtc_timer *timer);
+static int __rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled);
 
 static void rtc_add_offset(struct rtc_device *rtc, struct rtc_time *tm)
 {
@@ -81,6 +82,7 @@ static int rtc_valid_range(struct rtc_device *rtc, struct rtc_time *tm)
 	return 0;
 }
 
+/* This function must be called with rtc->ops_lock held */
 static int __rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
 {
 	int err;
@@ -553,27 +555,21 @@ int rtc_alarm_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 }
 EXPORT_SYMBOL_GPL(rtc_alarm_irq_enable);
 
-int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
+static int __rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 {
-	int err;
-
-	err = mutex_lock_interruptible(&rtc->ops_lock);
-	if (err)
-		return err;
+	int err = 0;
 
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
 	if (enabled == 0 && rtc->uie_irq_active) {
-		mutex_unlock(&rtc->ops_lock);
 		return rtc_dev_update_irq_enable_emul(rtc, 0);
 	}
 #endif
 	/* make sure we're changing state */
 	if (rtc->uie_rtctimer.enabled == enabled)
-		goto out;
+		return err;
 
 	if (!test_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features) ||
 	    !test_bit(RTC_FEATURE_ALARM, rtc->features)) {
-		mutex_unlock(&rtc->ops_lock);
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
 		return rtc_dev_update_irq_enable_emul(rtc, enabled);
 #else
@@ -587,7 +583,7 @@ int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 
 		err = __rtc_read_time(rtc, &tm);
 		if (err)
-			goto out;
+			return err;
 		onesec = ktime_set(1, 0);
 		now = rtc_tm_to_ktime(tm);
 		rtc->uie_rtctimer.node.expires = ktime_add(now, onesec);
@@ -597,7 +593,19 @@ int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
 		rtc_timer_remove(rtc, &rtc->uie_rtctimer);
 	}
 
-out:
+	return err;
+}
+
+int rtc_update_irq_enable(struct rtc_device *rtc, unsigned int enabled)
+{
+	int err;
+
+	err = mutex_lock_interruptible(&rtc->ops_lock);
+	if (err)
+		return err;
+
+	err = __rtc_update_irq_enable(rtc, enabled);
+
 	mutex_unlock(&rtc->ops_lock);
 
 	return err;
-- 
2.25.1