[Xen-devel] [PATCHv1 net] xen-netback: stop the guest rx thread after a fatal error

[David Vrabel <david.vrabel@xxxxxxxxxx>]

After commit e9d8b2c2968499c1f96563e6522c56958d5a1d0d (xen-netback:
disable rogue vif in kthread context), a fatal (protocol) error would
leave the guest Rx thread spinning, wasting CPU time.  Commit
ecf08d2dbb96d5a4b4bcc53a39e8d29cc8fef02e (xen-netback: reintroduce
guest Rx stall detection) made this even worse by removing a
cond_resched() from this path.

Since a fatal error is non-recoverable, just allow the guest Rx thread
to exit.  This requires taking additional refs to the task so the
thread exiting early is handled safely.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
Tested-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 drivers/net/xen-netback/interface.c |    2 ++
 drivers/net/xen-netback/netback.c   |    3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/xen-netback/interface.c 
b/drivers/net/xen-netback/interface.c
index 9259a73..037f74f 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -578,6 +578,7 @@ int xenvif_connect(struct xenvif_queue *queue, unsigned 
long tx_ring_ref,
                goto err_rx_unbind;
        }
        queue->task = task;
+       get_task_struct(task);
 
        task = kthread_create(xenvif_dealloc_kthread,
                              (void *)queue, "%s-dealloc", queue->name);
@@ -634,6 +635,7 @@ void xenvif_disconnect(struct xenvif *vif)
 
                if (queue->task) {
                        kthread_stop(queue->task);
+                       put_task_struct(queue->task);
                        queue->task = NULL;
                }
 
diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index 908e65e..c8ce701 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -2109,8 +2109,7 @@ int xenvif_kthread_guest_rx(void *data)
                 */
                if (unlikely(vif->disabled && queue->id == 0)) {
                        xenvif_carrier_off(vif);
-                       xenvif_rx_queue_purge(queue);
-                       continue;
+                       break;
                }
 
                if (!skb_queue_empty(&queue->rx_queue))
-- 
1.7.10.4


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