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

[Mathieu Desnoyers]

----- On Oct 6, 2017, at 5:08 PM, Paul E. McKenney paulmck at linux.vnet.ibm.com wrote:

> 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.

Hi Paul,

Given that the following patch in this patchset (2/2)
"Fix: membarrier: Handle CLONE_VM + !CLONE_THREAD correctly on powerpc"
is based on this patch, and that the fix needs to go into 4.14,
I would recommend queuing both patches for 4.14 is possible.

Otherwise I could try swapping the order of the two patches if
needed, but since both are touching nearby code areas, rebasing
is not straightforward.

Thanks,

Mathieu

> 
>							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

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com