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

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Message-ID: <YKyiKk6CAHq0+D9a@hirez.programming.kicks-ass.net>
Date:   Tue, 25 May 2021 09:07:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        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 Mon, May 24, 2021 at 03:41:50PM -0700, 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>

Thanks!