Messages in this thread | | | Subject | Re: [PATCH 7/7] xen/evtchn: read producer index only once | From | Jürgen Groß <> | Date | Mon, 8 Feb 2021 12:48:49 +0100 |
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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 <jgross@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).
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |