Re: PPPOE lockdep report in dev_queue_xmit+0x8b8/0x900

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

On Tue, 2013-02-19 at 13:10 +0200, Yanko Kaneti wrote:

> 
> It looks like it has done the job. I am running a kernel with the patch
> and workload that otherwise inevitably triggers the splat and so far it
> has been quiet.
> 

Thanks for testing.

David, there was a typo in the changelog : team should be replaced by
ppp.

[PATCH v2] ppp: set qdisc_tx_busylock to avoid LOCKDEP splat

If a qdisc is installed on a ppp device, its possible to get
a lockdep splat under stress, because nested dev_queue_xmit() can
lock busylock a second time (on a different device, so its a false
positive)

Avoid this problem using a distinct lock_class_key for ppp
devices.

Reported-by: Yanko Kaneti <yaneti@declera.com>
Tested-by: Yanko Kaneti <yaneti@declera.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/ppp/ppp_generic.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 4fd754e..3db9131 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -1058,7 +1058,15 @@ ppp_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats64)
 	return stats64;
 }
 
+static struct lock_class_key ppp_tx_busylock;
+static int ppp_dev_init(struct net_device *dev)
+{
+	dev->qdisc_tx_busylock = &ppp_tx_busylock;
+	return 0;
+}
+
 static const struct net_device_ops ppp_netdev_ops = {
+	.ndo_init	 = ppp_dev_init,
 	.ndo_start_xmit  = ppp_start_xmit,
 	.ndo_do_ioctl    = ppp_net_ioctl,
 	.ndo_get_stats64 = ppp_get_stats64,