Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH list

From: Randy Dunlap <rdunlap@infradead.org>
To: Waiman Long <llong@redhat.com>, Ingo Molnar <mingo@kernel.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
Subject: Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH list
Date: Mon, 24 May 2021 12:47:08 -0700	[thread overview]
Message-ID: <bfb11ab2-d606-b96e-1979-3bcc3c3adc96@infradead.org> (raw)
In-Reply-To: <1284b997-b9da-769f-2d36-4d4232c7df88@redhat.com>

On 5/17/21 7:02 AM, Waiman Long wrote:
> 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.

Yes, if we disregard the FRAME_POINTER part.

> Beside LOCKDEP, LATENCYTOP also have exactly the same depends-on line.

True, but I don't get any implication that the same patch applies there.
Do you?

> 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?

FRAME_POINTER is one way but it does not seem to be required
for STACKTRACE_SUPPORT.

Do you have any patch suggestions?

thanks.

-- 
~Randy