netdev - Re: CPU stalls with CONFIG_PREEMPT_RT enabled on next-20251006 (Renesas RZ/G2L & RZ/G3E)

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Message-ID: <5ac7ca4a-a85f-4611-92d6-fa1e26ee1c65@lunn.ch>
Date: Wed, 8 Oct 2025 01:04:05 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc: netdev <netdev@...r.kernel.org>,
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>
Subject: Re: CPU stalls with CONFIG_PREEMPT_RT enabled on next-20251006
 (Renesas RZ/G2L & RZ/G3E)

On Tue, Oct 07, 2025 at 10:40:59PM +0100, Lad, Prabhakar wrote:
> Hi Andrew,
> 
> On Tue, Oct 7, 2025 at 7:30 PM Andrew Lunn <andrew@...n.ch> wrote:
> >
> > On Tue, Oct 07, 2025 at 05:40:09PM +0100, Lad, Prabhakar wrote:
> > > Hi All,
> > >
> > > With CONFIG_PREEMPT_RT enabled, I’m observing CPU stalls from the Rx
> > > path on two different drivers across Renesas platforms.
> >
> > Do you have lockdep/CONFIG_PROVE_LOCKING enabled? Is this a deadlock?
> > Something else is already holding the lock?
> >
> I am using the ARM64 default defconfig with RT_PREEMPT enabled.
> 
> CONFIG_LOCKDEP_SUPPORT=y
> # CONFIG_PROVE_LOCKING is not set
> 
> I need to check if it's a deadlock, but from the looks of it does
> definitely look like something is already holding the lock.

Once you enable CONFIG_PROVE_LOCKING it should tell you about the
deadlock, a stack trace of the other locking path involved etc.

	Andrew