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

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Message-ID: <CA+V-a8v89b0Mg8ZX6nabNV8bMEan3EkonVhhHCb4t1GNxaxqrg@mail.gmail.com>
Date: Tue, 7 Oct 2025 22:40:59 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Andrew Lunn <andrew@...n.ch>
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)

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.

Cheers,
Prabhakar