Re: [PATCH 0/3] Kill off show_stack() NULL-implies-current idiom

From: Mark Rutland
Date: Mon Sep 26 2016 - 17:33:50 EST

On Mon, Sep 26, 2016 at 03:01:36PM -0500, Josh Poimboeuf wrote:
> On Mon, Sep 26, 2016 at 04:16:16PM +0100, Mark Rutland wrote:
> > Today, show_stack() accepts a NULL task parameter, which it takes to mean the
> > current task. However, as noted in tip/x86/asm commit:
> >
> > 81539169f283329f ("x86/dumpstack: Remove NULL task pointer convention")
> >
> > ... having a NULL task parameter imply current leads to subtle bugs in stack
> > walking code (so far seen on both 86 and arm64), makes callsites harder to
> > read, and is unnecessary as all callers have access to current.
> >
> > As a step towards removing the problematic NULL-implies-current idiom entirely,
> > these patches ensure that generic code explictly passes current to
> > show_stack(), rather than relying on arch code to handle NULL.
> This is a good step, though it would be really nice to fix this
> tree-wide. Do you have any plans to do so?

FWIW, I completely agree, though I have no plans to do so currently.

I'd meant to Cc linux-arch for this series in order to make people aware,
though evidently I did not. I can Cc subsequent arm64 NULL-implies-current
cleanup patches there, if that's helpful?

> Regardless, for the series:
> Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>