linux-kernel - [PATCH] virtio/ringtest: virtio_ring: fix up need

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Date:   Fri, 27 Oct 2017 16:11:13 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH] virtio/ringtest: virtio_ring: fix up need_event math

last kicked event index must be updated unconditionally:
even if we don't need to kick, we do not want to re-check
the same entry for events.

Reported-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 tools/virtio/ringtest/virtio_ring_0_9.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/tools/virtio/ringtest/virtio_ring_0_9.c b/tools/virtio/ringtest/virtio_ring_0_9.c
index bbc3043..5fd3fbc 100644
--- a/tools/virtio/ringtest/virtio_ring_0_9.c
+++ b/tools/virtio/ringtest/virtio_ring_0_9.c
@@ -225,16 +225,18 @@ bool enable_call()
 
 void kick_available(void)
 {
+	bool need;
+
 	/* Flush in previous flags write */
 	/* Barrier C (for pairing) */
 	smp_mb();
-	if (!vring_need_event(vring_avail_event(&ring),
-			      guest.avail_idx,
-			      guest.kicked_avail_idx))
-		return;
+	need = vring_need_event(vring_avail_event(&ring),
+				guest.avail_idx,
+				guest.kicked_avail_idx);
 
 	guest.kicked_avail_idx = guest.avail_idx;
-	kick();
+	if (need)
+		kick();
 }
 
 /* host side */
@@ -316,14 +318,16 @@ bool use_buf(unsigned *lenp, void **bufp)
 
 void call_used(void)
 {
+	bool need;
+
 	/* Flush in previous flags write */
 	/* Barrier D (for pairing) */
 	smp_mb();
-	if (!vring_need_event(vring_used_event(&ring),
-			      host.used_idx,
-			      host.called_used_idx))
-		return;
+	need = vring_need_event(vring_used_event(&ring),
+				host.used_idx,
+				host.called_used_idx);
 
 	host.called_used_idx = host.used_idx;
-	call();
+	if (need)
+		call();
 }
-- 
MST