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Mon, 24 May 2021 21:31:59 +0000 Subject: Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH list 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> From: Randy Dunlap Message-ID: Date: Mon, 24 May 2021 14:31:58 -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: <8a4ee5be-ad5c-ca06-dd1a-aa13ccc94906@redhat.com> 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 2:04 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. > 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. > > Cheers, > Longman > thanks. -- ~Randy