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virtio-balloon: fix add/get API use 

Since ee7cd8981e 'virtio: expose added
descriptors immediately.', in virtio balloon virtqueue_get_buf might
now run concurrently with virtqueue_kick.  I audited both and this
seems safe in practice but this is not guaranteed by the API.
Additionally, a spurious interrupt might in theory make
virtqueue_get_buf run in parallel with virtqueue_add_buf, which is
racy.

While we might try to protect against spurious callbacks it's
easier to fix the driver: balloon seems to be the only one
(mis)using the API like this, so let's just fix balloon.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (removed unused var)
This commit is contained in:
Michael S. Tsirkin 2012-07-02 10:33:08 +03:00 committed by Rusty Russell
parent 02edf6abe0
commit 9c378abc5c
1 changed files with 10 additions and 14 deletions
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24
drivers/virtio/virtio_balloon.c
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@ -47,7 +47,7 @@ struct virtio_balloon
struct task_struct *thread;
/* Waiting for host to ack the pages we released. */
struct completion acked;
wait_queue_head_t acked;
/* Number of balloon pages we've told the Host we're not using. */
unsigned int num_pages;
@ -89,29 +89,25 @@ static struct page *balloon_pfn_to_page(u32 pfn)
static void balloon_ack(struct virtqueue *vq)
{
struct virtio_balloon *vb;
unsigned int len;
struct virtio_balloon *vb = vq->vdev->priv;
vb = virtqueue_get_buf(vq, &len);
if (vb)
complete(&vb->acked);
wake_up(&vb->acked);
}
static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
{
struct scatterlist sg;
unsigned int len;
sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
init_completion(&vb->acked);
/* We should always be able to add one buffer to an empty queue. */
if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
BUG();
virtqueue_kick(vq);
/* When host has read buffer, this completes via balloon_ack */
wait_for_completion(&vb->acked);
wait_event(vb->acked, virtqueue_get_buf(vq, &len));
}
static void set_page_pfns(u32 pfns[], struct page *page)
@ -231,12 +227,8 @@ static void update_balloon_stats(struct virtio_balloon *vb)
*/
static void stats_request(struct virtqueue *vq)
{
struct virtio_balloon *vb;
unsigned int len;
struct virtio_balloon *vb = vq->vdev->priv;
vb = virtqueue_get_buf(vq, &len);
if (!vb)
return;
vb->need_stats_update = 1;
wake_up(&vb->config_change);
}
@ -245,11 +237,14 @@ static void stats_handle_request(struct virtio_balloon *vb)
{
struct virtqueue *vq;
struct scatterlist sg;
unsigned int len;
vb->need_stats_update = 0;
update_balloon_stats(vb);
vq = vb->stats_vq;
if (!virtqueue_get_buf(vq, &len))
return;
sg_init_one(&sg, vb->stats, sizeof(vb->stats));
if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
BUG();
@ -358,6 +353,7 @@ static int virtballoon_probe(struct virtio_device *vdev)
INIT_LIST_HEAD(&vb->pages);
vb->num_pages = 0;
init_waitqueue_head(&vb->config_change);
init_waitqueue_head(&vb->acked);
vb->vdev = vdev;
vb->need_stats_update = 0;