[3.16.y-ckt stable] Patch "net/xen-netfront: only napi_synchronize() if running" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    net/xen-netfront: only napi_synchronize() if running

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From a77af0e3b1e881b7cc74275764666ca846720097 Mon Sep 17 00:00:00 2001
From: Chas Williams <3chas3 at gmail.com>
Date: Thu, 27 Aug 2015 12:28:46 -0400
Subject: net/xen-netfront: only napi_synchronize() if running

commit 274b045509175db0405c784be85e8cce116e6f7d upstream.

If an interface isn't running napi_synchronize() will hang forever.

[  392.248403] rmmod           R  running task        0   359    343 0x00000000
[  392.257671]  ffff88003760fc88 ffff880037193b40 ffff880037193160 ffff88003760fc88
[  392.267644]  ffff880037610000 ffff88003760fcd8 0000000100014c22 ffffffff81f75c40
[  392.277524]  0000000000bc7010 ffff88003760fca8 ffffffff81796927 ffffffff81f75c40
[  392.287323] Call Trace:
[  392.291599]  [<ffffffff81796927>] schedule+0x37/0x90
[  392.298553]  [<ffffffff8179985b>] schedule_timeout+0x14b/0x280
[  392.306421]  [<ffffffff810f91b9>] ? irq_free_descs+0x69/0x80
[  392.314006]  [<ffffffff811084d0>] ? internal_add_timer+0xb0/0xb0
[  392.322125]  [<ffffffff81109d07>] msleep+0x37/0x50
[  392.329037]  [<ffffffffa00ec79a>] xennet_disconnect_backend.isra.24+0xda/0x390 [xen_netfront]
[  392.339658]  [<ffffffffa00ecadc>] xennet_remove+0x2c/0x80 [xen_netfront]
[  392.348516]  [<ffffffff81481c69>] xenbus_dev_remove+0x59/0xc0
[  392.356257]  [<ffffffff814e7217>] __device_release_driver+0x87/0x120
[  392.364645]  [<ffffffff814e7cf8>] driver_detach+0xb8/0xc0
[  392.371989]  [<ffffffff814e6e69>] bus_remove_driver+0x59/0xe0
[  392.379883]  [<ffffffff814e84f0>] driver_unregister+0x30/0x70
[  392.387495]  [<ffffffff814814b2>] xenbus_unregister_driver+0x12/0x20
[  392.395908]  [<ffffffffa00ed89b>] netif_exit+0x10/0x775 [xen_netfront]
[  392.404877]  [<ffffffff81124e08>] SyS_delete_module+0x1d8/0x230
[  392.412804]  [<ffffffff8179a8ee>] system_call_fastpath+0x12/0x71

Signed-off-by: Chas Williams <3chas3 at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Cc: Kamata, Munehisa <kamatam at amazon.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/net/xen-netfront.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 0838a2db5570..9d3bdea182cd 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1449,7 +1449,8 @@ static void xennet_disconnect_backend(struct netfront_info *info)
 		queue->tx_evtchn = queue->rx_evtchn = 0;
 		queue->tx_irq = queue->rx_irq = 0;

-		napi_synchronize(&queue->napi);
+		if (netif_running(info->netdev))
+			napi_synchronize(&queue->napi);

 		/* End access and free the pages */
 		xennet_end_access(queue->tx_ring_ref, queue->tx.sring);