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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH
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To:     Ingo Molnar <mingo@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>
Cc:     linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        linux-xtensa@linux-xtensa.org,
        Johannes Berg <johannes@sipsolutions.net>,
        Jeff Dike <jdike@addtoit.com>,
        Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        linux-um@lists.infradead.org
References: <20210517034430.9569-1-rdunlap@infradead.org>
 <YKIXBpxyvhzdb1uv@gmail.com>
Message-ID: <1284b997-b9da-769f-2d36-4d4232c7df88@redhat.com>
Date:   Mon, 17 May 2021 10:02:18 -0400
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On 5/17/21 3:11 AM, Ingo Molnar wrote:
> * Randy Dunlap <rdunlap@infradead.org> wrote:
>
>> Both arch/um/ and arch/xtensa/ cause a Kconfig warning for LOCKDEP.
>> These arch-es select LOCKDEP_SUPPORT but they are not listed as one
>> of the arch-es that LOCKDEP depends on.
>>
>> Since (16) arch-es define the Kconfig symbol LOCKDEP_SUPPORT if they
>> intend to have LOCKDEP support, replace the awkward list of
>> arch-es that LOCKDEP depends on with the LOCKDEP_SUPPORT symbol.
>>
>> Fixes this kconfig warning: (for both um and xtensa)
>>
>> WARNING: unmet direct dependencies detected for LOCKDEP
>>    Depends on [n]: DEBUG_KERNEL [=y] && LOCK_DEBUGGING_SUPPORT [=y] && (FRAME_POINTER [=n] || MIPS || PPC || S390 || MICROBLAZE || ARM || ARC || X86)
>>    Selected by [y]:
>>    - PROVE_LOCKING [=y] && DEBUG_KERNEL [=y] && LOCK_DEBUGGING_SUPPORT [=y]
>>    - LOCK_STAT [=y] && DEBUG_KERNEL [=y] && LOCK_DEBUGGING_SUPPORT [=y]
>>    - DEBUG_LOCK_ALLOC [=y] && DEBUG_KERNEL [=y] && LOCK_DEBUGGING_SUPPORT [=y]
>>
>> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Waiman Long <longman@redhat.com>
>> Cc: Boqun Feng <boqun.feng@gmail.com>
>> Cc: Chris Zankel <chris@zankel.net>
>> Cc: Max Filippov <jcmvbkbc@gmail.com>
>> Cc: linux-xtensa@linux-xtensa.org
>> Cc: Johannes Berg <johannes@sipsolutions.net>
>> Cc: Jeff Dike <jdike@addtoit.com>
>> Cc: Richard Weinberger <richard@nod.at>
>> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
>> Cc: linux-um@lists.infradead.org
>> ---
>>   lib/Kconfig.debug |    2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- linux-next-20210514.orig/lib/Kconfig.debug
>> +++ linux-next-20210514/lib/Kconfig.debug
>> @@ -1383,7 +1383,7 @@ config LOCKDEP
>>   	bool
>>   	depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
>>   	select STACKTRACE
>> -	depends on FRAME_POINTER || MIPS || PPC || S390 || MICROBLAZE || ARM || ARC || X86
>> +	depends on FRAME_POINTER || LOCKDEP_SUPPORT
> Ok - the FRAME_POINTER bit is weird. Are there any architectures that have
> FRAME_POINTER defined but no LOCKDEP_SUPPORT?

LOCK_DEBUGGING_SUPPORT depends on LOCKDEP_SUPPORT. So this patch is 
equivalent to just delete the second depends-on line. Beside LOCKDEP, 
LATENCYTOP also have exactly the same depends-on line.

So isn't FRAME_POINTER used mainly to support STACK_TRACE? However, 
LOCK_DEBUGGING_SUPPORT has already included STACK_TRACE_SUPPORT in its 
dependency. So why there is a FRAME_POINTER dependency?

Cheers,
Longman