linux-kernel - Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock

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Message-ID: <20241127165356.hnkqmgcc@linutronix.de>
Date: Wed, 27 Nov 2024 17:53:56 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Andreas Larsson <andreas@...sler.com>, Waiman Long <llong@...hat.com>,
	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock_t.

On 2024-11-27 08:02:50 [-0800], Guenter Roeck wrote:
> On 11/27/24 07:39, Andreas Larsson wrote:
> > Even though this is for sparc64, there is work being done looking into
> > enabling RT for sparc32. If the amount of fixes needed to keep
> > PROVE_RAW_LOCK_NESTING enabled is quite small at the moment I'd rather
> > see it enabled for sparc rather than risking it becoming worse in the
> > future.

Okay. So you seem to be in favour of fixing the sparc64 splats Guenter
reported?

> > I don't know what the situation is for other architectures that does not
> > support RT.
> > 
> 
> For my part I still don't understand why PROVE_RAW_LOCK_NESTING is no longer
> a configurable option, or in other words why it is mandated even for architectures
> not supporting RT. To me this means that I'll either have to disable PROVE_LOCKING
> for sparc or live with endless warning backtraces. The latter obscures real
> problems, so it is a no-go.

It is documented in Documentation/locking/locktypes.rst how the locks
should nest. It is just nobody enabled it on sparc64 and tested. The
option was meant temporary until the big read blocks are cleared.

> So, if people want to keep mandating PROVE_RAW_LOCK_NESTING together with
> PROVE_LOCKING for all architectures, I'll disable PROVE_LOCKING for sparc
> in my testing. NP, just let me know. I'll then do the same for other
> architectures not supporting RT if I hit the same problem there.

Waiman posted a patch to disable it on architectures that don't support
PREEMPT_RT. You could also post the patches you discussed. Andreas does
not seem to be against it (but then I don't know if he is a 32 or 64bit
guy). I did not year from other architectures so far.

> Guenter

Sebastian