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

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Message-Id: <20171005223327.3500-1-mathieu.desnoyers@efficios.com>
Date:   Thu,  5 Oct 2017 18:33:26 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        Maged Michael <maged.michael@...il.com>, gromer@...gle.com,
        Avi Kivity <avi@...lladb.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Dave Watson <davejwatson@...com>,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linuxppc-dev@...ts.ozlabs.org, linux-arch@...r.kernel.org
Subject: [RFC PATCH for 4.14 1/2] membarrier: Remove unused code for architectures without membarrier hooks

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@...il.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@...il.com>
CC: Andrew Hunter <ahh@...gle.com>
CC: Maged Michael <maged.michael@...il.com>
CC: gromer@...gle.com
CC: Avi Kivity <avi@...lladb.com>
CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC: Paul Mackerras <paulus@...ba.org>
CC: Michael Ellerman <mpe@...erman.id.au>
CC: Dave Watson <davejwatson@...com>
CC: Alan Stern <stern@...land.harvard.edu>
CC: Will Deacon <will.deacon@....com>
CC: Andy Lutomirski <luto@...nel.org>
CC: Ingo Molnar <mingo@...hat.com>
CC: Alexander Viro <viro@...iv.linux.org.uk>
CC: linuxppc-dev@...ts.ozlabs.org
CC: linux-arch@...r.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