* xen-netfront: bug with napi_synchronize()
@ 2015-08-20 20:50 Charles (Chas) Williams
0 siblings, 0 replies; only message in thread
From: Charles (Chas) Williams @ 2015-08-20 20:50 UTC (permalink / raw)
To: netdev; +Cc: xen-devel
I have seen some hangs in recent versions of the xen-netfront driver.
If I unload or unbind the driver immediately befor bringing up the
interface, I get a hang as show in the traceback here.
...
[ 194.037351] [<ffffffff810ae1a7>] ? msleep+0x27/0x30
[ 194.037358] [<ffffffffa004b48a>] ? xennet_disconnect_backend+0xfa/0x390 [xen_netfront]
[ 194.037364] [<ffffffffa004b789>] ? xennet_remove+0x19/0x60 [xen_netfront]
[ 194.037368] [<ffffffff8132971b>] ? xenbus_dev_remove+0x4b/0xa0
[ 194.037375] [<ffffffff8137bf41>] ? __device_release_driver+0x81/0x120
[ 194.037378] [<ffffffff8137bffd>] ? device_release_driver+0x1d/0x30
[ 194.037382] [<ffffffff8137b340>] ? unbind_store+0xf0/0x150
...
This offset in xennet_disconnect_backend is approximately in the area
of napi_synchronize(). napi_synchronize() does contain an msleep()
and nothing else would really sleep in this routine.
queue->tx_evtchn = queue->rx_evtchn = 0;
queue->tx_irq = queue->rx_irq = 0;
napi_synchronize(&queue->napi);
xennet_release_tx_bufs(queue);
xennet_release_rx_bufs(queue);
Since I never started the interface, I know napi_enable() was never
called on queue->napi. However, what is the expected behavior for
napi_synchronize() on something that was never enabled/disabled?
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