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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aIvCE4x24RigKBKF@shell.armlinux.org.uk>
Date: Thu, 31 Jul 2025 20:20:51 +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 06:03:43PM +0100, Mark Brown wrote:
> On Thu, Jul 31, 2025 at 05:28:39PM +0100, Russell King (Oracle) wrote:
> > On Thu, Jul 31, 2025 at 05:16:13PM +0100, Mark Brown wrote:
> 
> > > Yeah, and that's all internals which we're not super encouraged to peer
> > > at.  There should be something that'll give us a nesting level
> > > somewhere...  
> 
> > > Lockdep's handling of nesting is generally fun.
> 
> > As I said, I'm just going to disable lockdep to shut up the warning and
> > not pursue any further time on this. If someone else cares about it
> > (which I doubt) they can try to come up with a solution. I suspect
> > nested regmap-irq is extremely rare.
> 
> I'm pretty sure it's extremely rare, and I'll have to construct a
> virtual setup to actually test.  After poking at it some more I think
> we're actually going to need an explicit lock_class_key for each
> regmap-irq rather than relying on the default lockdep one.  I'll try to
> send out a patch for that today or tomorrow but likely not really tested
> - if you could find time to give it a spin on the affected system that'd
> be good, but if not no worries.  Thanks for the report and analysis.

I hope we don't have too many regmap-irq's in a system - see the
section on "Troubleshooting" in the lockdep documentation. There's
a limit on the numbe of classes over the entire kernel.

For reference, on the platform which provokes this lockdep splat,
we already have 1518 lock classes:

# grep "lock-classes" /proc/lockdep_stats
 lock-classes:                         1518 [max: 8192]

As I understand from the documentation, lock classes are create-only,
there's no way of "freeing" them later, so we better not get into a
situation where the number of classes steadily increase while the
system is running!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!