Re: [PATCH v10 01/11] arm64: Select STACKTRACE in arch/arm64/Kconfig

Mark Rutland
2021-11-12T17:44:17Z

On Fri, Oct 22, 2021 at 07:02:43PM +0100, Mark Rutland wrote:
> On Thu, Oct 14, 2021 at 09:58:37PM -0500, madvenka@linux.microsoft.com wrote:
> > From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
> >
> > Currently, there are multiple functions in ARM64 code that walk the
> > stack using start_backtrace() and unwind_frame() or start_backtrace()
> > and walk_stackframe(). They should all be converted to use
> > arch_stack_walk(). This makes maintenance easier.
> >
> > To do that, arch_stack_walk() must always be defined. arch_stack_walk()
> > is within #ifdef CONFIG_STACKTRACE. So, select STACKTRACE in
> > arch/arm64/Kconfig.
>
> I'd prefer if we could decouple ARCH_STACKWALK from STACKTRACE, so that
> we don't have to expose /proc/*/stack unconditionally, which Peter
> Zijlstra has a patch for:
>
> https://lore.kernel.org/lkml/20211022152104.356586621@infradead.org/
>
> ... but regardless the rest of the series looks pretty good, so I'll go
> review that, and we can figure out how to queue the bits and pieces in
> the right order.

FWIW, it looks like the direction of travel there is not go and unify
the various arch unwinders, but I would like to not depend on
STACKTRACE. Regardless, the initial arch_stack_walk() cleanup patches
all look good, so I reckon we should try to get those out of the way and
queue those for arm64 soon even if we need some more back-and-forth over
the later part of the series.

With that in mind, I've picked up Peter's patch decoupling
ARCH_STACKWALK from STACKTRACE, and rebased the initial patches from
this series atop. Since there's some subtltety in a few cases (and this
was easy to miss while reviewing), I've expanded the commit messages
with additional rationale as to why each transformation is safe.
I've pushed that to:

https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/stacktrace/arch-stack-walk

There's a dependency on:

https://lore.kernel.org/r/20211029162245.39761-1-mark.rutland@arm.com

... which was queued for v5.16-rc1, but got dropped due to a conflict,
and I'm expecting it to be re-queued as a fix for v5.16-rc2 shortly
after v5.16-rc1 is tagged. Hopefully that means we have a table base by
v5.16-rc2.

I'll send the preparatory series as I've prepared it shortly after
v5.16-rc1 so that people can shout if I've messed something up.

Hopefully it's easy enough to use that as a base for the more involved
rework later in this series.

Thanks,
Mark.

> Thanks,
> Mark.
>
> >
> > Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
> > ---
> > arch/arm64/Kconfig | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index fdcd54d39c1e..bfb0ce60d820 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -35,6 +35,7 @@ config ARM64
> > select ARCH_HAS_SET_DIRECT_MAP
> > select ARCH_HAS_SET_MEMORY
> > select ARCH_STACKWALK
> > + select STACKTRACE
> > select ARCH_HAS_STRICT_KERNEL_RWX
> > select ARCH_HAS_STRICT_MODULE_RWX
> > select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> > --
> > 2.25.1
> >