linux-kernel - [PATCH] events/uprobes: move smp_read_barrier

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Date:	Thu,  9 Jun 2016 20:18:41 +0200
From:	Andrea Parri <parri.andrea@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrea Parri <parri.andrea@...il.com>
Subject: [PATCH] events/uprobes: move smp_read_barrier_depends() where needed

There is no need to use the barrier if there is no dereference/
memory access; move it where needed (currently, affecting only
Alpha). While touching this, also make the reads _ONCE().

Signed-off-by: Andrea Parri <parri.andrea@...il.com>
---
 kernel/events/uprobes.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index b7a525ab2083..b1364acd683e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1520,10 +1520,11 @@ static unsigned long get_trampoline_vaddr(void)
 	struct xol_area *area;
 	unsigned long trampoline_vaddr = -1;
 
-	area = current->mm->uprobes_state.xol_area;
-	smp_read_barrier_depends();
-	if (area)
-		trampoline_vaddr = area->vaddr;
+	area = READ_ONCE(current->mm->uprobes_state.xol_area);
+	if (area) {
+		smp_read_barrier_depends();
+		trampoline_vaddr = READ_ONCE(area->vaddr);
+	}
 
 	return trampoline_vaddr;
 }
-- 
1.9.1