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commit00a39d8652upstream. 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 commit6950d046eb("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 commit13be2efc39("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>