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

[Waiman Long]

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 <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.
> 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

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.

> > 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.
> > 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"):

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