linux-kernel - [DRAFT PATCH] rtc-cmos: use spin_lock_irqsave in cmos

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Message-Id: <20250602202019.625331-1-mat.jonczyk@o2.pl>
Date: Mon,  2 Jun 2025 22:20:19 +0200
From: Mateusz Jończyk <mat.jonczyk@...pl>
To: Chris Bainbridge <chris.bainbridge@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	linux-rtc@...r.kernel.org,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mateusz Jończyk <mat.jonczyk@...pl>
Subject: [DRAFT PATCH] rtc-cmos: use spin_lock_irqsave in cmos_interrupt

cmos_interrupt() can also be called also in non-interrupt contexts, such
as in ACPI handlers via rtc_handler(). Therefore, usage of
spin_lock(&rtc_lock) is insecure. Use spin_lock_irqsave() / etc.
instead.

Remove the local_irq_disable() hacks in cmos_check_wkalrm() and add a
comment so that these _irqsave / _irqrestore will not be disabled again,
as in

commit 6950d046eb6e ("rtc: cmos: Replace spin_lock_irqsave with spin_lock in hard IRQ")

Untested yet.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
Fixes: 13be2efc390a ("rtc: cmos: Disable irq around direct invocation of cmos_interrupt()")
---
 drivers/rtc/rtc-cmos.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 8172869bd3d7..399bb82e6153 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -692,8 +692,12 @@ static irqreturn_t cmos_interrupt(int irq, void *p)
 {
 	u8		irqstat;
 	u8		rtc_control;
+	unsigned long	flags;
 
-	spin_lock(&rtc_lock);
+	/* We cannot use spin_lock() here, as cmos_interrupt() is also called
+	 * in non-irq context.
+	 */
+	spin_lock_irqsave(&rtc_lock, flags);
 
 	/* When the HPET interrupt handler calls us, the interrupt
 	 * status is passed as arg1 instead of the irq number.  But
@@ -727,7 +731,7 @@ static irqreturn_t cmos_interrupt(int irq, void *p)
 			hpet_mask_rtc_irq_bit(RTC_AIE);
 		CMOS_READ(RTC_INTR_FLAGS);
 	}
-	spin_unlock(&rtc_lock);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	if (is_intr(irqstat)) {
 		rtc_update_irq(p, 1, irqstat);
@@ -1295,9 +1299,7 @@ static void cmos_check_wkalrm(struct device *dev)
 	 * ACK the rtc irq here
 	 */
 	if (t_now >= cmos->alarm_expires && cmos_use_acpi_alarm()) {
-		local_irq_disable();
 		cmos_interrupt(0, (void *)cmos->rtc);
-		local_irq_enable();
 		return;
 	}
 
-- 
2.25.1