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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c029c2fd-8bac-4913-b98f-f09acd7d28e1@redhat.com>
Date: Wed, 27 Nov 2024 18:47:08 -0500
From: Waiman Long <llong@...hat.com>
To: Guenter Roeck <linux@...ck-us.net>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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 11/27/24 12:44 PM, Guenter Roeck wrote:
> On 11/27/24 08:53, Sebastian Andrzej Siewior wrote:
>> 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.
>>
>
> That doesn't explain why PROVE_RAW_LOCK_NESTING is now mandatory if
> PROVE_LOCKING is enabled, even on architectures where is was not tested.
> I am all for testing, but that doesn't include making it mandatory
> even where it is known to fail. Enabling it by default, sure, no problem.
> Dropping the option entirely after it is proven to no longer needed,
> also no problem. But force-enabling it even where untested or, worse,
> known to fail, is two steps too far.

The main reason for enforcing PROVE_RAW_LOCK_NESTING with PROVE_LOCKING 
is due to the fact that PREEMPT_RT kernel is much less tested than the 
non-RT kernel. I do agree that we shouldn't force this on arches that 
don't support PREEMPT_RT. However, once an arch decides to support 
PREEMPT_RT, they have to fix all these raw_spinlock nesting problems.

Cheers,
Longman