xen/netback: Wake dealloc thread after completing zerocopy work

Waking the dealloc thread before decrementing inflight_packets is racy
because it means the thread may go to sleep before inflight_packets is
decremented. If kthread_stop() has already been called, the dealloc
thread may wait forever with nothing to wake it. Instead, wake the
thread only after decrementing inflight_packets.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index 1a83e19..28577a3 100644 (file)
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -61,6 +61,12 @@ void xenvif_skb_zerocopy_prepare(struct xenvif_queue *queue,
 void xenvif_skb_zerocopy_complete(struct xenvif_queue *queue)
 {
        atomic_dec(&queue->inflight_packets);
+
+       /* Wake the dealloc thread _after_ decrementing inflight_packets so
+        * that if kthread_stop() has already been called, the dealloc thread
+        * does not wait forever with nothing to wake it.
+        */
+       wake_up(&queue->dealloc_wq);
 }
 
 int xenvif_schedulable(struct xenvif *vif)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 1b406e7..3f44b52 100644 (file)
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1541,7 +1541,6 @@ void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success)
                smp_wmb();
                queue->dealloc_prod++;
        } while (ubuf);
-       wake_up(&queue->dealloc_wq);
        spin_unlock_irqrestore(&queue->callback_lock, flags);
 
        if (likely(zerocopy_success))