2015-11-20 15:03:35

by Stefano Stabellini

Subject: [PATCH] xen/time: use READ_ONCE

Use READ_ONCE through the code, rather than explicit barriers.

Suggested-by: Mark Rutland <[email protected]>
Signed-off-by: Stefano Stabellini <[email protected]>
CC: Mark Rutland <[email protected]>
CC: [email protected]
CC: [email protected]
CC: [email protected]
---
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

2015-11-26 17:46:28

by David Vrabel

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

On 20/11/15 15:02, Stefano Stabellini wrote:
> Use READ_ONCE through the code, rather than explicit barriers.

Applied to for-linus-4.5, thanks.

David