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

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Message-ID: <2a940822-b4d4-43ea-b4f7-4294043b76ea@roeck-us.net>
Date: Mon, 25 Nov 2024 12:23:04 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Waiman Long <llong@...hat.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: 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>,
 Andreas Larsson <andreas@...sler.com>
Subject: Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock_t.

On 11/25/24 12:06, Guenter Roeck wrote:
> On 11/25/24 11:33, Waiman Long wrote:
> [ ... ]
>>> Fixing that finally gives me a clean run. Nevertheless, that makes me wonder:
>>> Should I just disable CONFIG_PROVE_RAW_LOCK_NESTING for sparc runtime tests ?
>>
>> If no one is tryng to ever enable PREEMPT_RT on SPARC, I suppose you could disable CONFIG_PROVE_RAW_LOCK_NESTING to avoid the trouble.
>>
> 
> SGTM. I'll do that unless someone gives me a good reason to keep it enabled.
> 

Actually it can not be disabled with a configuration flag. It is
automatically enabled. I'll have to disable PROVE_LOCKING to disable it.

config PROVE_RAW_LOCK_NESTING
         bool					<---- no longer user configurable
         depends on PROVE_LOCKING
         default y
         help
          Enable the raw_spinlock vs. spinlock nesting checks which ensure
          that the lock nesting rules for PREEMPT_RT enabled kernels are
          not violated.

I don't really like that, and I don't understand the logic behind it,
but it is what it is.

FWIW, the description of commit 560af5dc839 is misleading. It says "Enable
PROVE_RAW_LOCK_NESTING _by default_" (emphasis mine). That is not what the
commit does. It force-enables PROVE_RAW_LOCK_NESTING if PROVE_LOCKING is
enabled. It is all or nothing.

Guenter