linux-kernel - Re: [PATCH] thread_info: include <current.h> for THREAD_INFO_IN_TASK (WAS: [PATCH 2/3] sched/preempt: include asm/current.h)

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Date:   Tue, 18 Oct 2016 12:34:40 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] thread_info: include <current.h> for THREAD_INFO_IN_TASK
 (WAS: [PATCH 2/3] sched/preempt: include asm/current.h)

On Mon, Oct 17, 2016 at 06:33:15PM +0100, Mark Rutland wrote:
> On Mon, Oct 17, 2016 at 03:48:13PM +0100, Mark Rutland wrote:
> > On Fri, Oct 14, 2016 at 11:42:25AM +0100, Mark Rutland 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.
> > > 
> > > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > > ---
> > >  include/linux/thread_info.h | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > As discussed, it would be great if this could go in along with the patch to
> > > make thread_info arch-specific again, to make merging the arch-specific parts
> > > easier (for arm64 and s390).
> > 
> > Urrgh; I've just recalled that this patch alone is insufficient. The
> > h8300 arch code has an unfixed bug [1], and relies on some implicit
> > definition ordering that will be broken by this patch.
> > 
> > I have a workaround/cleanup for core code that I'll send with an updated
> > version of my arm64 series shortly.
> 
> Looks like I spoke too soon. I have another circular include issue with
> raw_smp_processor_id() and task_struct::cpu to solve -- it looks like
> s390 doesn't suffer from that per my reading of your headers.

That's correct.

> In the mean time, I've pushed out a branch [2] with the common patches,
> atop of v4.9-rc1.

I just verified that your branch works fine for s390 (with and without the
THREAD_INFO_IN_TASK conversion).

Thanks,
Heiko