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([2601:408:c180:2530:d041:4c25:86b8:e76a]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6d8751f7221sm850936d6.91.2024.11.27.15.47.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Nov 2024 15:47:10 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Wed, 27 Nov 2024 18:47:08 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sparc/pci: Make pci_poke_lock a raw_spinlock_t. To: Guenter Roeck , Sebastian Andrzej Siewior Cc: Andreas Larsson , Waiman Long , sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, Boqun Feng , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Will Deacon , "David S. Miller" References: <20241125181231.XpOsxxHx@linutronix.de> <72991b83-173e-492e-a4aa-5049304c1bd0@roeck-us.net> <5d269249-afd1-44f5-8faf-9ac11d9a3beb@redhat.com> <2a940822-b4d4-43ea-b4f7-4294043b76ea@roeck-us.net> <88f47cea-baba-4673-9bd7-7b7c3f421008@redhat.com> <20241126112000.UkTwR0Iv@linutronix.de> <48b9d642-9739-4333-b4b9-319df8a85e2d@redhat.com> <4eb7bb8e-c2aa-4ce5-9f15-3086fccf4e46@roeck-us.net> <20241127165356.hnkqmgcc@linutronix.de> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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