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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Message-ID: <20161017173315.GB23170@leverpostej>
Date:   Mon, 17 Oct 2016 18:33:15 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Heiko Carstens <heiko.carstens@...ibm.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 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.

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

Thanks,
Mark.

[1] http://lkml.kernel.org/r/<1476714934-11635-1-git-send-email-mark.rutland@....com
[2] https://git.kernel.org/cgit/linux/kernel/git/mark/linux.git/log/?h=core/ti-stack-split