virtio/ringtest: virtio_ring: fix up need_event math

Web:        https://git.kernel.org/torvalds/c/a311650ae6ad0c169ade2583f78aa519878ea13f
Commit:     a311650ae6ad0c169ade2583f78aa519878ea13f
Parent:     f229a55c31a7e12a15c7b4dcf9a97a9bf7a72ce8
Refname:    refs/heads/master
Author:     Michael S. Tsirkin <[email protected]>
AuthorDate: Fri Oct 27 16:11:13 2017 +0300
Committer:  Michael S. Tsirkin <[email protected]>
CommitDate: Wed Jan 31 01:47:36 2018 +0200

    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 <[email protected]>
    Signed-off-by: Michael S. Tsirkin <[email protected]>
    Reviewed-by: Jens Freimann <[email protected]>
---
 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 bbc3043b2fb1..5fd3fbcb9e57 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();
 }
--
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