[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH 7/7] xen/evtchn: read producer index only once
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:For consistency, don't you also need the write side in evtchn_interrupt() to use WRITE_ONCE()?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);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
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