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Mon, 24 May 2021 21:41:55 +0000 Subject: Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH list From: Randy Dunlap To: Waiman Long , Ingo Molnar Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Johannes Berg , Jeff Dike , Richard Weinberger , Anton Ivanov , linux-um@lists.infradead.org References: <20210517034430.9569-1-rdunlap@infradead.org> <1284b997-b9da-769f-2d36-4d4232c7df88@redhat.com> <8a4ee5be-ad5c-ca06-dd1a-aa13ccc94906@redhat.com> Message-ID: <09243238-94ba-caca-441e-3fdac0154822@infradead.org> Date: Mon, 24 May 2021 14:41:52 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/24/21 2:31 PM, Randy Dunlap wrote: > On 5/24/21 2:04 PM, Waiman Long wrote: >> On 5/24/21 3:47 PM, Randy Dunlap wrote: >>> On 5/17/21 7:02 AM, Waiman Long wrote: >>>> On 5/17/21 3:11 AM, Ingo Molnar wrote: >>>>> * Randy Dunlap 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 >>>>>> Cc: Peter Zijlstra >>>>>> Cc: Ingo Molnar >>>>>> Cc: Will Deacon >>>>>> Cc: Waiman Long >>>>>> Cc: Boqun Feng >>>>>> Cc: Chris Zankel >>>>>> Cc: Max Filippov >>>>>> Cc: linux-xtensa@linux-xtensa.org >>>>>> Cc: Johannes Berg >>>>>> Cc: Jeff Dike >>>>>> Cc: Richard Weinberger >>>>>> Cc: Anton Ivanov >>>>>> 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. >> >> My understanding is that the 2 depends-on statements have an implicit AND. So it is like > > Right (on the implicit AND). > >> DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT && (FRAME_POINTER || LOCKDEP_SUPPORT). LOCK_DEBUGGING_SUPPORT is true means the (FRAME_POINTER || LOCKDEP_SUPPORT) will always be true. FRAME_POINTER is true doesn't mean the other dependencies are true. That is why I said it is equivalent to just "DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT". IOW, FRAME_POINTER will play no part here. >> > > Ack. I should have done that myself. > >>> >>>> 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? >> It is just an observation that I stumble on. It is not related to your patch. > > Got it. > >>>> 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? >> >> 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 <<<<<<<<<<< >> 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 && >> +       depends on FRAME_POINTER || MIPS || PPC || S390 || MICROBLAZE || ARM || >>         select KALLSYMS >>         select KALLSYMS_ALL >> >> Since STACKTRACE is selected by lockdep, maybe we can just remove the 2nd depends-on line to see if anyone complain. -- ~Randy