From 2840cf02fae627860156737e83326df354ee4ec6 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 19 Sep 2019 13:37:01 -0400
Subject: [PATCH] sched/membarrier: Call sync_core only before usermode for
same mm
When the prev and next task's mm change, switch_mm() provides the core
serializing guarantees before returning to usermode. The only case
where an explicit core serialization is needed is when the scheduler
keeps the same mm for prev and next.
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190919173705.2181-4-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/sched/mm.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 4a7944078cc35..8557ec6642130 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -362,6 +362,8 @@ enum {
static inline void membarrier_mm_sync_core_before_usermode(struct mm_struct *mm)
{
+ if (current->mm != mm)
+ return;
if (likely(!(atomic_read(&mm->membarrier_state) &
MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE)))
return;
--
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