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rtc: cmos: use spin_lock_irqsave in cmos_interrupt

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commit 00a39d8652ff9088de07a6fe6e9e1893452fe0dd upstream.

cmos_interrupt() can be called in a non-interrupt context, such as in
an ACPI event handler (which runs in an interrupt thread). Therefore,
usage of spin_lock(&rtc_lock) is insecure. Use spin_lock_irqsave() /
spin_unlock_irqrestore() instead.

Before a misguided
commit 6950d046eb ("rtc: cmos: Replace spin_lock_irqsave with spin_lock in hard IRQ")
the cmos_interrupt() function used spin_lock_irqsave(). That commit
changed it to spin_lock() and broke locking, which was partially fixed in
commit 13be2efc39 ("rtc: cmos: Disable irq around direct invocation of cmos_interrupt()")

That second commit did not take account of the ACPI fixed event handler
pathway, however. It introduced local_irq_disable() workarounds in
cmos_check_wkalrm(), which can cause problems on PREEMPT_RT kernels
and are now unnecessary.

Add an explicit comment so that this change will not be reverted by
mistake.

Cc: stable@vger.kernel.org
Fixes: 6950d046eb ("rtc: cmos: Replace spin_lock_irqsave with spin_lock in hard IRQ")
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Reported-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Closes: https://lore.kernel.org/all/aDtJ92foPUYmGheF@debian.local/
Link: https://lore.kernel.org/r/20250607210608.14835-1-mat.jonczyk@o2.pl
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mateusz Jończyk
2025-06-07 23:06:08 +02:00
committed by Greg Kroah-Hartman
parent 5cdd1f7340
commit 39617dc3fa
1 changed files with 6 additions and 4 deletions
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10
drivers/rtc/rtc-cmos.c
View File

@@ -697,8 +697,12 @@ static irqreturn_t cmos_interrupt(int irq, void *p)
{ {
u8 irqstat; u8 irqstat;
u8 rtc_control; u8 rtc_control;
unsigned long flags;
spin_lock(&rtc_lock); /* We cannot use spin_lock() here, as cmos_interrupt() is also called
* in a non-irq context.
*/
spin_lock_irqsave(&rtc_lock, flags);
/* When the HPET interrupt handler calls us, the interrupt /* When the HPET interrupt handler calls us, the interrupt
* status is passed as arg1 instead of the irq number. But * status is passed as arg1 instead of the irq number. But
@@ -732,7 +736,7 @@ static irqreturn_t cmos_interrupt(int irq, void *p)
hpet_mask_rtc_irq_bit(RTC_AIE); hpet_mask_rtc_irq_bit(RTC_AIE);
CMOS_READ(RTC_INTR_FLAGS); CMOS_READ(RTC_INTR_FLAGS);
} }
spin_unlock(&rtc_lock); spin_unlock_irqrestore(&rtc_lock, flags);
if (is_intr(irqstat)) { if (is_intr(irqstat)) {
rtc_update_irq(p, 1, irqstat); rtc_update_irq(p, 1, irqstat);
@@ -1300,9 +1304,7 @@ static void cmos_check_wkalrm(struct device *dev)
* ACK the rtc irq here * ACK the rtc irq here
*/ */
if (t_now >= cmos->alarm_expires && cmos_use_acpi_alarm()) { if (t_now >= cmos->alarm_expires && cmos_use_acpi_alarm()) {
local_irq_disable();
cmos_interrupt(0, (void *)cmos->rtc); cmos_interrupt(0, (void *)cmos->rtc);
local_irq_enable();
return; return;
} }