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

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Date:   Mon, 24 May 2021 15:41:50 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Peter Zijlstra <peterz@...radead.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: [PATCH v2] LOCKDEP: reduce LOCKDEP dependency list

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