[Xen-devel] [PATCH] xen/time: use READ_ONCE

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Use READ_ONCE through the code, rather than explicit barriers.

Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CC: Mark Rutland <mark.rutland@xxxxxxx>
CC: konrad.wilk@xxxxxxxxxx
CC: david.vrabel@xxxxxxxxxx
CC: boris.ostrovsky@xxxxxxxxxx
---
 drivers/xen/time.c |   17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/xen/time.c b/drivers/xen/time.c
index 433fe24..7107842 100644
--- a/drivers/xen/time.c
+++ b/drivers/xen/time.c
@@ -25,7 +25,7 @@ static u64 get64(const u64 *p)
 
        if (BITS_PER_LONG < 64) {
                u32 *p32 = (u32 *)p;
-               u32 h, l;
+               u32 h, l, h2;
 
                /*
                 * Read high then low, and then make sure high is
@@ -34,15 +34,14 @@ static u64 get64(const u64 *p)
                 * XXX some clean way to make this endian-proof?
                 */
                do {
-                       h = p32[1];
-                       barrier();
-                       l = p32[0];
-                       barrier();
-               } while (p32[1] != h);
+                       h = READ_ONCE(p32[1]);
+                       l = READ_ONCE(p32[0]);
+                       h2 = READ_ONCE(p32[1]);
+               } while(h2 != h);
 
                ret = (((u64)h) << 32) | l;
        } else
-               ret = *p;
+               ret = READ_ONCE(*p);
 
        return ret;
 }
@@ -66,9 +65,7 @@ void xen_get_runstate_snapshot(struct vcpu_runstate_info *res)
         */
        do {
                state_time = get64(&state->state_entry_time);
-               barrier();
-               *res = *state;
-               barrier();
+               *res = READ_ONCE(*state);
        } while (get64(&state->state_entry_time) != state_time);
 }
 
-- 
1.7.10.4


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