[PATCH] events/uprobes: move smp_read_barrier_depends() where needed

From	Andrea Parri <parri.andrea@gmail.com>
Newsgroups	linux.kernel
Subject	[PATCH] events/uprobes: move smp_read_barrier_depends() where needed
Date	2016-06-09 20:20 +0200
Message-ID	<rIcIF-1zJ-1@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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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@gmail.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

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[PATCH] events/uprobes: move smp_read_barrier_depends() where needed Andrea Parri <parri.andrea@gmail.com> - 2016-06-09 20:20 +0200
  Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 09:10 +0200
    Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 14:30 +0200
      Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 15:10 +0200
        Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 16:50 +0200
          Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 21:40 +0200
    Re: [PATCH] events/uprobes: move smp_read_barrier_depends() where  needed Oleg Nesterov <oleg@redhat.com> - 2016-06-10 15:00 +0200

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