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

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Message-ID: <88f47cea-baba-4673-9bd7-7b7c3f421008@redhat.com>
Date: Mon, 25 Nov 2024 15:54:48 -0500
From: Waiman Long <llong@...hat.com>
To: Guenter Roeck <linux@...ck-us.net>, 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 3:23 PM, Guenter Roeck wrote:
> 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.
>
I think we can relax it by

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5d9eca035d47..bfdbd3fa2d29 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1399,7 +1399,7 @@ config PROVE_LOCKING
  config PROVE_RAW_LOCK_NESTING
         bool
         depends on PROVE_LOCKING
-       default y
+       default y if ARCH_SUPPORTS_RT
         help
          Enable the raw_spinlock vs. spinlock nesting checks which ensure
          that the lock nesting rules for PREEMPT_RT enabled kernels are

Sebastian, what do you think?

Cheers,
Longman

> Guenter
>