linux-kernel - Re: [PATCH v2] LOCKDEP: reduce LOCKDEP dependency list

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Date:   Tue, 25 May 2021 10:17:57 -0400
From:   Waiman Long <llong@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     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, Julian Braha <julianbraha@...il.com>,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v2] LOCKDEP: reduce LOCKDEP dependency list

On 5/24/21 6:41 PM, Randy Dunlap wrote:
> Some arches (um, sparc64, riscv, 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.
>
> But wait. LOCKDEP_SUPPORT is included in LOCK_DEBUGGING_SUPPORT,
> which is already a dependency here, so LOCKDEP_SUPPORT is redundant
> and not needed.
> That leaves the FRAME_POINTER dependency, but it is part of an
> expression like this:
> 	depends on (A && B) && (FRAME_POINTER || B')
> where B' is a dependency of B so if B is true then B' is true
> and the value of FRAME_POINTER does not matter.
> Thus we can also delete the FRAME_POINTER dependency.
>
> Fixes this kconfig warning: (for um, sparc64, riscv, 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]
>
> Link to v1: https://lore.kernel.org/lkml/20210517034430.9569-1-rdunlap@infradead.org/
>
> Fixes: 7d37cb2c912d ("lib: fix kconfig dependency on ARCH_WANT_FRAME_POINTERS")
> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Chris Zankel <chris@...kel.net>
> Cc: Max Filippov <jcmvbkbc@...il.com>
> Cc: linux-xtensa@...ux-xtensa.org
> Cc: Johannes Berg <johannes@...solutions.net>
> Cc: Jeff Dike <jdike@...toit.com>
> Cc: Richard Weinberger <richard@....at>
> Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
> Cc: linux-um@...ts.infradead.org
> Cc: Julian Braha <julianbraha@...il.com>
> Cc: linux-arch@...r.kernel.org
> ---
> @Julian: please take a look. I'm a little concerned about the
>    FRAME_POINTER dependency going away when our 2 patches are combined.
>
> v2: drop depends on LOCKDEP_SUPPORT for LOCKDEP; the use of
>      LOCK_DEBUGGING_SUPPORT already covers that dependency;
>      drop FRAME_POINTER dependency (thanks to Waiman Long
>      for both of these suggestions)
> v2: add CC: to linux-arch
>
>   lib/Kconfig.debug |    1 -
>   1 file changed, 1 deletion(-)
>
> --- linux-next-20210524.orig/lib/Kconfig.debug
> +++ linux-next-20210524/lib/Kconfig.debug
> @@ -1383,7 +1383,6 @@ config LOCKDEP
>   	bool
>   	depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
>   	select STACKTRACE
> -	depends on FRAME_POINTER || MIPS || PPC || S390 || MICROBLAZE || ARM || ARC || X86
>   	select KALLSYMS
>   	select KALLSYMS_ALL
>   
>
Acked-by: Waiman Long <longman@...hat.com>

Cheers,
Longman