Re: [PATCH 7/7] xen/evtchn: read producer index only once
From: Julien Grall
Date: Mon Feb 08 2021 - 07:03:40 EST
On 06/02/2021 10:49, Juergen Gross wrote:
In evtchn_read() use READ_ONCE() for reading the producer index in
order to avoid the compiler generating multiple accesses.
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
drivers/xen/evtchn.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index 421382c73d88..f6b199b597bf 100644
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -211,7 +211,7 @@ static ssize_t evtchn_read(struct file *file, char __user *buf,
goto unlock_out;
c = u->ring_cons;
- p = u->ring_prod;
+ p = READ_ONCE(u->ring_prod);
For consistency, don't you also need the write side in
evtchn_interrupt() to use WRITE_ONCE()?
if (c != p)
break;
--
Julien Grall