linux-kernel - [PATCH 4.14 28/91] drm/virtio: fix vq wait

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Date:   Mon, 30 Apr 2018 12:24:10 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alain Magloire <amagloire@...ckberry.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Dave Airlie <airlied@...hat.com>,
        Sean Paul <seanpaul@...omium.org>
Subject: [PATCH 4.14 28/91] drm/virtio: fix vq wait_event condition

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gerd Hoffmann <kraxel@...hat.com>

commit d02d270014f70dcab0117776b81a37b6fca745ae upstream.

Wait until we have enough space in the virt queue to actually queue up
our request.  Avoids the guest spinning in case we have a non-zero
amount of free entries but not enough for the request.

Cc: stable@...r.kernel.org
Reported-by: Alain Magloire <amagloire@...ckberry.com>
Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
Reviewed-by: Dave Airlie <airlied@...hat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180403095904.11152-1-kraxel@redhat.com
Signed-off-by: Sean Paul <seanpaul@...omium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/virtio/virtgpu_vq.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -291,7 +291,7 @@ retry:
 	ret = virtqueue_add_sgs(vq, sgs, outcnt, incnt, vbuf, GFP_ATOMIC);
 	if (ret == -ENOSPC) {
 		spin_unlock(&vgdev->ctrlq.qlock);
-		wait_event(vgdev->ctrlq.ack_queue, vq->num_free);
+		wait_event(vgdev->ctrlq.ack_queue, vq->num_free >= outcnt + incnt);
 		spin_lock(&vgdev->ctrlq.qlock);
 		goto retry;
 	} else {
@@ -366,7 +366,7 @@ retry:
 	ret = virtqueue_add_sgs(vq, sgs, outcnt, 0, vbuf, GFP_ATOMIC);
 	if (ret == -ENOSPC) {
 		spin_unlock(&vgdev->cursorq.qlock);
-		wait_event(vgdev->cursorq.ack_queue, vq->num_free);
+		wait_event(vgdev->cursorq.ack_queue, vq->num_free >= outcnt);
 		spin_lock(&vgdev->cursorq.qlock);
 		goto retry;
 	} else {