[RFC PATCH for 4.14 1/2] membarrier: Remove unused code for architectures without membarrier hooks

[Paul E. McKenney]

On Thu, Oct 05, 2017 at 06:33:26PM -0400, Mathieu Desnoyers wrote:
> Architectures without membarrier hooks don't need to emit the
> empty membarrier_arch_switch_mm() static inline when
> CONFIG_MEMBARRIER=y.
> 
> Adapt the CONFIG_MEMBARRIER=n counterpart to only emit the empty
> membarrier_arch_switch_mm() for architectures with membarrier hooks.
> 
> Reported-by: Nicholas Piggin <npiggin at gmail.com>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

Queued for further review and testing, targeting v4.15.  Please let me
know if you need it sooner.

							Thanx, Paul

> CC: Peter Zijlstra <peterz at infradead.org>
> CC: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> CC: Boqun Feng <boqun.feng at gmail.com>
> CC: Andrew Hunter <ahh at google.com>
> CC: Maged Michael <maged.michael at gmail.com>
> CC: gromer at google.com
> CC: Avi Kivity <avi at scylladb.com>
> CC: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> CC: Paul Mackerras <paulus at samba.org>
> CC: Michael Ellerman <mpe at ellerman.id.au>
> CC: Dave Watson <davejwatson at fb.com>
> CC: Alan Stern <stern at rowland.harvard.edu>
> CC: Will Deacon <will.deacon at arm.com>
> CC: Andy Lutomirski <luto at kernel.org>
> CC: Ingo Molnar <mingo at redhat.com>
> CC: Alexander Viro <viro at zeniv.linux.org.uk>
> CC: linuxppc-dev at lists.ozlabs.org
> CC: linux-arch at vger.kernel.org
> ---
>  include/linux/sched/mm.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index d5a9ab8f3836..b2767ecb21a8 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -215,10 +215,6 @@ static inline void memalloc_noreclaim_restore(unsigned int flags)
>  #ifdef CONFIG_ARCH_HAS_MEMBARRIER_HOOKS
>  #include <asm/membarrier.h>
>  #else
> -static inline void membarrier_arch_switch_mm(struct mm_struct *prev,
> -		struct mm_struct *next, struct task_struct *tsk)
> -{
> -}
>  static inline void membarrier_arch_fork(struct task_struct *t,
>  		unsigned long clone_flags)
>  {
> @@ -247,10 +243,12 @@ static inline void membarrier_execve(struct task_struct *t)
>  	membarrier_arch_execve(t);
>  }
>  #else
> +#ifdef CONFIG_ARCH_HAS_MEMBARRIER_HOOKS
>  static inline void membarrier_arch_switch_mm(struct mm_struct *prev,
>  		struct mm_struct *next, struct task_struct *tsk)
>  {
>  }
> +#endif
>  static inline void membarrier_fork(struct task_struct *t,
>  		unsigned long clone_flags)
>  {
> -- 
> 2.11.0
>