[PATCH tip/core/rcu 09/21] uprobes: Remove now-redundant smp_read_barrier_depends()

From: Paul E. McKenney
Date: Fri Dec 01 2017 - 14:55:05 EST


Now that READ_ONCE() implies smp_read_barrier_depends(), the
get_xol_area() and get_trampoline_vaddr() no longer need their
smp_read_barrier_depends() calls, which this commit removes.
While we are here, convert the corresponding smp_wmb() to an
smp_store_release().

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
---
kernel/events/uprobes.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 267f6ef91d97..ce6848e46e94 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1167,8 +1167,8 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
}

ret = 0;
- smp_wmb(); /* pairs with get_xol_area() */
- mm->uprobes_state.xol_area = area;
+ /* pairs with get_xol_area() */
+ smp_store_release(&mm->uprobes_state.xol_area, area); /* ^^^ */
fail:
up_write(&mm->mmap_sem);

@@ -1230,8 +1230,8 @@ static struct xol_area *get_xol_area(void)
if (!mm->uprobes_state.xol_area)
__create_xol_area(0);

- area = mm->uprobes_state.xol_area;
- smp_read_barrier_depends(); /* pairs with wmb in xol_add_vma() */
+ /* Pairs with xol_add_vma() smp_store_release() */
+ area = READ_ONCE(mm->uprobes_state.xol_area); /* ^^^ */
return area;
}

@@ -1528,8 +1528,8 @@ 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();
+ /* Pairs with xol_add_vma() smp_store_release() */
+ area = READ_ONCE(current->mm->uprobes_state.xol_area); /* ^^^ */
if (area)
trampoline_vaddr = area->vaddr;

--
2.5.2