hv_netvsc: Fix panic during namespace deletion with VF

The existing code move the VF NIC to new namespace when NETDEV_REGISTER is
received on netvsc NIC. During deletion of the namespace,
default_device_exit_batch() >> default_device_exit_net() is called. When
netvsc NIC is moved back and registered to the default namespace, it
automatically brings VF NIC back to the default namespace. This will cause
the default_device_exit_net() >> for_each_netdev_safe loop unable to detect
the list end, and hit NULL ptr:

[  231.449420] mana 7870:00:00.0 enP30832s1: Moved VF to namespace with: eth0
[  231.449656] BUG: kernel NULL pointer dereference, address: 0000000000000010
[  231.450246] #PF: supervisor read access in kernel mode
[  231.450579] #PF: error_code(0x0000) - not-present page
[  231.450916] PGD 17b8a8067 P4D 0
[  231.451163] Oops: Oops: 0000 [#1] SMP NOPTI
[  231.451450] CPU: 82 UID: 0 PID: 1394 Comm: kworker/u768:1 Not tainted 6.16.0-rc4+ #3 VOLUNTARY
[  231.452042] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 11/21/2024
[  231.452692] Workqueue: netns cleanup_net
[  231.452947] RIP: 0010:default_device_exit_batch+0x16c/0x3f0
[  231.453326] Code: c0 0c f5 b3 e8 d5 db fe ff 48 85 c0 74 15 48 c7 c2 f8 fd ca b2 be 10 00 00 00 48 8d 7d c0 e8 7b 77 25 00 49 8b 86 28 01 00 00 <48> 8b 50 10 4c 8b 2a 4c 8d 62 f0 49 83 ed 10 4c 39 e0 0f 84 d6 00
[  231.454294] RSP: 0018:ff75fc7c9bf9fd00 EFLAGS: 00010246
[  231.454610] RAX: 0000000000000000 RBX: 0000000000000002 RCX: 61c8864680b583eb
[  231.455094] RDX: ff1fa9f71462d800 RSI: ff75fc7c9bf9fd38 RDI: 0000000030766564
[  231.455686] RBP: ff75fc7c9bf9fd78 R08: 0000000000000000 R09: 0000000000000000
[  231.456126] R10: 0000000000000001 R11: 0000000000000004 R12: ff1fa9f70088e340
[  231.456621] R13: ff1fa9f70088e340 R14: ffffffffb3f50c20 R15: ff1fa9f7103e6340
[  231.457161] FS:  0000000000000000(0000) GS:ff1faa6783a08000(0000) knlGS:0000000000000000
[  231.457707] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  231.458031] CR2: 0000000000000010 CR3: 0000000179ab2006 CR4: 0000000000b73ef0
[  231.458434] Call Trace:
[  231.458600]  <TASK>
[  231.458777]  ops_undo_list+0x100/0x220
[  231.459015]  cleanup_net+0x1b8/0x300
[  231.459285]  process_one_work+0x184/0x340

To fix it, move the ns change to a workqueue, and take rtnl_lock to avoid
changing the netdev list when default_device_exit_net() is using it.

Cc: [email protected]
Fixes: 4c26280 ("hv_netvsc: Fix VF namespace also in synthetic NIC NETDEV_REGISTER event")
Signed-off-by: Haiyang Zhang <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: haiyangz

drivers/net/hyperv/hyperv_net.h

@@ -1061,6 +1061,7 @@ struct net_device_context {
 	struct net_device __rcu *vf_netdev;
 	struct netvsc_vf_pcpu_stats __percpu *vf_stats;
 	struct delayed_work vf_takeover;
+	struct delayed_work vfns_work;
 
 	/* 1: allocated, serial number is valid. 0: not allocated */
 	u32 vf_alloc;
@@ -1075,6 +1076,8 @@ struct net_device_context {
 	struct netvsc_device_info *saved_netvsc_dev_info;
 };
 
+void netvsc_vfns_work(struct work_struct *w);
+
 /* Azure hosts don't support non-TCP port numbers in hashing for fragmented
  * packets. We can use ethtool to change UDP hash level when necessary.
  */

drivers/net/hyperv/netvsc_drv.c

@@ -2522,6 +2522,7 @@ static int netvsc_probe(struct hv_device *dev,
 	spin_lock_init(&net_device_ctx->lock);
 	INIT_LIST_HEAD(&net_device_ctx->reconfig_events);
 	INIT_DELAYED_WORK(&net_device_ctx->vf_takeover, netvsc_vf_setup);
+	INIT_DELAYED_WORK(&net_device_ctx->vfns_work, netvsc_vfns_work);
 
 	net_device_ctx->vf_stats
 		= netdev_alloc_pcpu_stats(struct netvsc_vf_pcpu_stats);
@@ -2666,6 +2667,8 @@ static void netvsc_remove(struct hv_device *dev)
 	cancel_delayed_work_sync(&ndev_ctx->dwork);
 
 	rtnl_lock();
+	cancel_delayed_work_sync(&ndev_ctx->vfns_work);
+
 	nvdev = rtnl_dereference(ndev_ctx->nvdev);
 	if (nvdev) {
 		cancel_work_sync(&nvdev->subchan_work);
@@ -2707,6 +2710,7 @@ static int netvsc_suspend(struct hv_device *dev)
 	cancel_delayed_work_sync(&ndev_ctx->dwork);
 
 	rtnl_lock();
+	cancel_delayed_work_sync(&ndev_ctx->vfns_work);
 
 	nvdev = rtnl_dereference(ndev_ctx->nvdev);
 	if (nvdev == NULL) {
@@ -2800,6 +2804,27 @@ static void netvsc_event_set_vf_ns(struct net_device *ndev)
 	}
 }
 
+void netvsc_vfns_work(struct work_struct *w)
+{
+	struct net_device_context *ndev_ctx =
+		container_of(w, struct net_device_context, vfns_work.work);
+	struct net_device *ndev;
+
+	if (!rtnl_trylock()) {
+		schedule_delayed_work(&ndev_ctx->vfns_work, 1);
+		return;
+	}
+
+	ndev = hv_get_drvdata(ndev_ctx->device_ctx);
+	if (!ndev)
+		goto out;
+
+	netvsc_event_set_vf_ns(ndev);
+
+out:
+	rtnl_unlock();
+}
+
 /*
  * On Hyper-V, every VF interface is matched with a corresponding
  * synthetic interface. The synthetic interface is presented first
@@ -2810,10 +2835,12 @@ static int netvsc_netdev_event(struct notifier_block *this,
 			       unsigned long event, void *ptr)
 {
 	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
+	struct net_device_context *ndev_ctx;
 	int ret = 0;
 
 	if (event_dev->netdev_ops == &device_ops && event == NETDEV_REGISTER) {
-		netvsc_event_set_vf_ns(event_dev);
+		ndev_ctx = netdev_priv(event_dev);
+		schedule_delayed_work(&ndev_ctx->vfns_work, 0);
 		return NOTIFY_DONE;
 	}