Commit d072218f authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by David S. Miller
Browse files

hv_netvsc: avoid deadlocks between rtnl lock and vf_use_cnt wait 



Here is a deadlock scenario:
- netvsc_vf_up() schedules netvsc_notify_peers() work and quits.
- netvsc_vf_down() runs before netvsc_notify_peers() gets executed. As it
  is being executed from netdev notifier chain we hold rtnl lock when we
  get here.
- we enter while (atomic_read(&net_device_ctx->vf_use_cnt) != 0) loop and
  wait till netvsc_notify_peers() drops vf_use_cnt.
- netvsc_notify_peers() starts on some other CPU but netdev_notify_peers()
  will hang on rtnl_lock().
- deadlock!

Instead of introducing additional synchronization I suggest we drop
gwrk.dwrk completely and call NETDEV_NOTIFY_PEERS directly. As we're
acting under rtnl lock this is legitimate.

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: default avatarHaiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f9a7da91

drivers/net/hyperv/hyperv_net.h

+0 −7
Original line number Diff line number Diff line
@@ -644,12 +644,6 @@ struct netvsc_reconfig { 
	u32 event;

};



struct garp_wrk {

	struct work_struct dwrk;

	struct net_device *netdev;

	struct net_device_context *net_device_ctx;

};



/* The context of the netvsc device  */

struct net_device_context {

	/* point back to our device context */
@@ -667,7 +661,6 @@ struct net_device_context { 


	struct work_struct work;

	u32 msg_enable; /* debug level */

	struct garp_wrk gwrk;



	struct netvsc_stats __percpu *tx_stats;

	struct netvsc_stats __percpu *rx_stats;

drivers/net/hyperv/netvsc_drv.c

+5 −28
Original line number Diff line number Diff line
@@ -1151,17 +1151,6 @@ static void netvsc_free_netdev(struct net_device *netdev) 
	free_netdev(netdev);

}



static void netvsc_notify_peers(struct work_struct *wrk)

{

	struct garp_wrk *gwrk;



	gwrk = container_of(wrk, struct garp_wrk, dwrk);



	netdev_notify_peers(gwrk->netdev);



	atomic_dec(&gwrk->net_device_ctx->vf_use_cnt);

}



static struct net_device *get_netvsc_net_device(char *mac)

{

	struct net_device *dev, *found = NULL;
@@ -1253,15 +1242,8 @@ static int netvsc_vf_up(struct net_device *vf_netdev) 


	netif_carrier_off(ndev);



	/*

	 * Now notify peers. We are scheduling work to

	 * notify peers; take a reference to prevent

	 * the VF interface from vanishing.

	 */

	atomic_inc(&net_device_ctx->vf_use_cnt);

	net_device_ctx->gwrk.netdev = vf_netdev;

	net_device_ctx->gwrk.net_device_ctx = net_device_ctx;

	schedule_work(&net_device_ctx->gwrk.dwrk);

	/* Now notify peers through VF device. */

	call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, vf_netdev);



	return NOTIFY_OK;

}
@@ -1300,13 +1282,9 @@ static int netvsc_vf_down(struct net_device *vf_netdev) 
	netdev_info(ndev, "Data path switched from VF: %s\n", vf_netdev->name);

	rndis_filter_close(netvsc_dev);

	netif_carrier_on(ndev);

	/*

	 * Notify peers.

	 */

	atomic_inc(&net_device_ctx->vf_use_cnt);

	net_device_ctx->gwrk.netdev = ndev;

	net_device_ctx->gwrk.net_device_ctx = net_device_ctx;

	schedule_work(&net_device_ctx->gwrk.dwrk);



	/* Now notify peers through netvsc device. */

	call_netdevice_notifiers(NETDEV_NOTIFY_PEERS, ndev);



	return NOTIFY_OK;

}
@@ -1378,7 +1356,6 @@ static int netvsc_probe(struct hv_device *dev, 


	INIT_DELAYED_WORK(&net_device_ctx->dwork, netvsc_link_change);

	INIT_WORK(&net_device_ctx->work, do_set_multicast);

	INIT_WORK(&net_device_ctx->gwrk.dwrk, netvsc_notify_peers);



	spin_lock_init(&net_device_ctx->lock);

	INIT_LIST_HEAD(&net_device_ctx->reconfig_events);

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