linux-kernel - Re: [-next] Lockdep warnings

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Date:   Tue, 26 Jul 2022 15:54:30 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sudeep Holla <sudeep.holla@....com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [-next] Lockdep warnings

On Tue, Jul 26, 2022 at 03:44:31PM +0100, Mark Rutland wrote:
> On Tue, Jul 26, 2022 at 11:41:34AM +0100, Sudeep Holla wrote:
> > I was seeing the below lockdep warnings on my arm64 Juno development
> > platform almost 2 weeks back with -next. I wanted to check for similar
> > reports before post and forgot.
> 
> [...]
> 
> > However I don't see the above warning with the latest -next. When I tried
> > yesterday's -next now, I see a different warning. Not sure if they are
> > related. I haven't tried to bisect.
> > 
> > --->8
> > =============================
> > [ BUG: Invalid wait context ]
> > 5.19.0-rc8-next-20220725 #38 Not tainted
> > -----------------------------
> > swapper/0/0 is trying to lock:
> > (&drvdata->spinlock){....}-{3:3}, at: cti_cpu_pm_notify+0x54/0x114
> 
> Hmmm... do you have CONFIG_PROVE_RAW_LOCK_NESTING enabled?
>

Yes.

> IIUC that should be {2:2} otherwise...
> 
> > other info that might help us debug this:
> > context-{5:5}
> > 1 lock held by swapper/0/0:
> >  #0: (cpu_pm_notifier.lock){....}-{2:2}, at: cpu_pm_enter+0x2c/0x80
> 
> ... and this is telling us that we're trying to take a regular spinlock under a
> raw spinlock, which is not as intended.
> 
> The Kconfig text notes:
> 
>          NOTE: There are known nesting problems. So if you enable this 
>          option expect lockdep splats until these problems have been fully
>          addressed which is work in progress. This config switch allows to
>          identify and analyze these problems. It will be removed and the
>          check permanently enabled once the main issues have been fixed.
> 

Ah, I hadn't seen or read this. Thanks for digging this and sharing.
Sorry for the noise. Good I got to know this limitation, will try to
remember this.

Thanks again for your time Mark.

-- 
Regards,
Sudeep