linux-kernel - Re: [PATCH 3/3] thread_info: include <current.h> for THREAD_INFO_IN

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Date:   Fri, 28 Oct 2016 11:48:06 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kees Cook <keescook@...omium.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] thread_info: include <current.h> for
 THREAD_INFO_IN_TASK

On Thu, Oct 27, 2016 at 04:13:49PM -0700, Andy Lutomirski wrote:
> On Wed, Oct 19, 2016 at 11:28 AM, Mark Rutland <mark.rutland@....com> wrote:
> > When CONFIG_THREAD_INFO_IN_TASK is selected, the current_thread_info()
> > macro relies on current having been defined prior to its use. However,
> > not all users of current_thread_info() include <asm/current.h>, and thus
> > current is not guaranteed to be defined.
> >
> > When CONFIG_THREAD_INFO_IN_TASK is not selected, it's possible that
> > get_current() / current are based upon current_thread_info(), and
> > <asm/current.h> includes <asm/thread_info.h>. Thus always including
> > <asm/current.h> would result in circular dependences on some platforms.
> >
> > To ensure both cases work, this patch includes <asm/current.h>, but only
> > when CONFIG_THREAD_INFO_IN_TASK is selected.
> 
> Reviewed-by: Andy Lutomirski <luto@...nel.org>

Cheers!

> although it would be nice if you moved your description of why the
> include is conditional into a comment.

Agreed. I've folded in the below:

#ifdef CONFIG_THREAD_INFO_IN_TASK
/*
 * For CONFIG_THREAD_INFO_IN_TASK kernels we need <asm/current.h> for the
 * definition of current, but for !CONFIG_THREAD_INFO_IN_TASK kernels,
 * including <asm/current.h> can cause a circular dependency on some platforms.
 */
#include <asm/current.h>
#define current_thread_info() ((struct thread_info *)current)
#endif

Thanks,
Mark.