Hi Juergen,
On 08/02/2021 11:48, Jürgen Groß wrote:
On 08.02.21 12:40, Julien Grall wrote:
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 <jgr...@suse.com>
---
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()?
Only in case I'd consider the compiler needing multiple memory
accesses for doing the update (see my reply to Jan's comment on this
patch).
Right, I have just answered there :). AFAICT, without using
WRITE_ONCE()/READ_ONCE() there is no guarantee that load/store tearing
will not happen.
We can continue the conversation there.
Cheers,
Juergen
--
Julien Grall
