linux-kernel - Re: [PATCH] LOCKDEP: use depends on LOCKDEP

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Message-ID: <38797295-8c65-814a-c550-298da324b988@redhat.com>
Date:   Tue, 25 May 2021 10:15:47 -0400
From:   Waiman Long <llong@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        Waiman Long <llong@...hat.com>, Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org,
        Johannes Berg <johannes@...solutions.net>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        linux-um@...ts.infradead.org
Subject: Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH
 list

On 5/25/21 12:18 AM, Randy Dunlap wrote:
> On 5/24/21 5:05 PM, Waiman Long wrote:
>> On 5/24/21 5:41 PM, Randy Dunlap wrote:
>>> On 5/24/21 2:31 PM, Randy Dunlap wrote:
>>>> On 5/24/21 2:04 PM, Waiman Long wrote:
>>>>
>>>>> Is it possible to just get rid of the 2nd depends-on statement?
>>>>>
>>>>> The 2nd depends-on line was introduced by commit 7d37cb2c912d ("lib: fix kconfig dependency on ARCH_WANT_FRAME_POINTER"):
>>>> and I should have looked at that history too. Thanks.
>>>>
>>>> Yes, I agree, we can just delete that line...
>>>>
>>>> I'll send a v2 and copy the author of commit 7d37cb2c912d as well.
>>> Hm, as I review that commit, I have to wonder if the previous 'select'
>>> was correct (if we disregard the Kconfig warning).  If so, then
>>> FRAME_POINTER is still wanted/needed for some arch-es.
>>>
>>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>>> index 2779c29d9981..417c3d3e521b 100644
>>> --- a/lib/Kconfig.debug
>>> +++ b/lib/Kconfig.debug
>>> @@ -1363,7 +1363,7 @@ config LOCKDEP
>>>           bool
>>>           depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
>>>           select STACKTRACE
>>> -       select FRAME_POINTER if !MIPS && !PPC && !ARM && !S390 && !MICROBLAZE && !ARC && !X86 <<<<<<<<<<<
>>>
>> AFAICS, enabling FRAME_POINTER is a debugging aid as it enable more precise stacktrace. However, not all archs want to enable FRAME_POINTER because of LOCKDEP. Now you are just letting users decide if they want FRAME_POINTER or not. Maybe you can modify the help text to mention that.
> LOCKDEP doesn't have any user help text.
>
> For FRAME_POINTER, when ARCH_WANT_FRAME_POINTERS + a few other conditions
> is met, it seems that the FRAME_POINTER help text is good enough IMO.
>
> 	help
> 	  If you say Y here the resulting kernel image will be slightly
> 	  larger and slower, but it gives very useful debugging information
> 	  in case of kernel bugs. (precise oopses/stacktraces/warnings)
>
Right. I am fine with that.

Thanks,
Longman