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

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Date:   Mon, 24 May 2021 20:05:51 -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 5/24/21 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.

Cheers,
Longman