linux-kernel - [PATCH 7/7] xen/evtchn: read producer index only once

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Date:   Sat,  6 Feb 2021 11:49:32 +0100
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: [PATCH 7/7] xen/evtchn: read producer index only 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@...e.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);
 		if (c != p)
 			break;
 
-- 
2.26.2