linux-kernel - Re: [BUG] 6.16-rc7: lockdep failure with max77620-gpio/max77686-rtc

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Message-ID: <aIuSdnV8sWnUqLOq@shell.armlinux.org.uk>
Date: Thu, 31 Jul 2025 16:57:42 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Mark Brown <broonie@...nel.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>, linux-gpio@...r.kernel.org,
	linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thierry Reding <treding@...dia.com>
Subject: Re: [BUG] 6.16-rc7: lockdep failure with max77620-gpio/max77686-rtc

On Thu, Jul 31, 2025 at 02:18:24PM +0100, Mark Brown wrote:
> On Thu, Jul 31, 2025 at 01:43:14PM +0100, Russell King (Oracle) wrote:
> > On Thu, Jul 31, 2025 at 01:31:32PM +0100, Mark Brown wrote:
> 
> > > Yes, your analysis is right here - it's not come up before because it's
> > > very rare to chain regmap-irq chips.
> 
> > Yep, I just changed all the "d" variables in regmap-irq to "ricd"
> > (first letter of the each word of the struct name), and lockdep
> > confirms that it's the mutex.
> 
> > I'm not familiar enough with lockdep to know how to fix this, so what's
> > the solution here?
> 
> I *think* mutex_lock_nested() is what we're looking for here, with the
> depth information from the irq_desc but I'm also not super familiar with
> this stuff.

I'm not sure about that, because the irq_desc locks don't nest:

        raw_spin_lock_init(&desc->lock);
        lockdep_set_class(&desc->lock, &irq_desc_lock_class);

What saves irq_desc lock nesting in this case is that
__irq_put_desc_unlock() unlocks desc->lock calling the
irq_bus_sync_unlock() method. So, I don't think we have anything at
the irq_desc level which deals with lock-nesting.

I guess I'll just ignore the lockdep warning or turn lockdep off,
one or other is probably like everyone else does.

-- 
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