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

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Message-ID: <20160927175720.GA4479@remoulade>
Date:   Tue, 27 Sep 2016 18:57:20 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 0/3] Kill off show_stack() NULL-implies-current idiom

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?

I started having a go, and in doing so I've realised that as things stand,
these patches are broken, as some architectures don't handle current
explicitly.

Please disregard all patches in this series.

Apologies,
Mark.