Re: [PATCH] LOCKDEP: use depends on LOCKDEP_SUPPORT instead of $ARCH list

[Waiman Long]

On 5/17/21 3:11 AM, Ingo Molnar wrote:
> * Randy Dunlap <rdunlap@xxxxxxxxxxxxx> 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 <rdunlap@xxxxxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Waiman Long <longman@xxxxxxxxxx>
> > Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> > Cc: Chris Zankel <chris@xxxxxxxxxx>
> > Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
> > Cc: linux-xtensa@xxxxxxxxxxxxxxxx
> > Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> > Cc: Jeff Dike <jdike@xxxxxxxxxxx>
> > Cc: Richard Weinberger <richard@xxxxxx>
> > Cc: Anton Ivanov <anton.ivanov@xxxxxxxxxxxxxxxxxx>
> > Cc: linux-um@xxxxxxxxxxxxxxxxxxx
> > ---
> >   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. Beside LOCKDEP, 
LATENCYTOP also have exactly the same depends-on line.

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?

Cheers,
Longman