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

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Message-ID: <20250603064722.xpshWggM@linutronix.de>
Date: Tue, 3 Jun 2025 08:47:22 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Mateusz Jończyk <mat.jonczyk@...pl>
Cc: Chris Bainbridge <chris.bainbridge@...il.com>,
	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>
Subject: Re: [DRAFT PATCH] rtc-cmos: use spin_lock_irqsave in cmos_interrupt

On 2025-06-02 22:20:19 [+0200], Mateusz Jończyk wrote:
> 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

This also broke PREEMPT_RT due to disable-IRQ -> spinlock_t.

> 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()")

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Sebastian