[PATCH net] hv_netvsc: Switch VF namespace in netvsc_open instead

[PATCH net] hv_netvsc: Switch VF namespace in netvsc_open instead

[Haiyang Zhang]

From: Haiyang Zhang <haiyangz@microsoft.com>

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 VF namespace switching code from the NETDEV_REGISTER
event handler to netvsc_open().


Cc: stable@vger.kernel.org
Fixes: 4c262801ea60 ("hv_netvsc: Fix VF namespace also in synthetic NIC NETDEV_REGISTER event")
Reported-by: Cathy Avery <cavery@redhat.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 43 ++++++++++-----------------------
 1 file changed, 13 insertions(+), 30 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 42d98e99566e..074ecc346108 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -135,6 +135,19 @@ static int netvsc_open(struct net_device *net)
 	}
 
 	if (vf_netdev) {
+		if (!net_eq(dev_net(net), dev_net(vf_netdev))) {
+			ret = dev_change_net_namespace(vf_netdev, dev_net(net),
+						       "eth%d");
+			if (ret)
+				netdev_err(vf_netdev,
+					   "Cannot move to same ns as %s: %d\n",
+					   net->name, ret);
+			else
+				netdev_info(vf_netdev,
+					    "Moved VF to namespace with: %s\n",
+					    net->name);
+		}
+
 		/* Setting synthetic device up transparently sets
 		 * slave as up. If open fails, then slave will be
 		 * still be offline (and not used).
@@ -2772,31 +2785,6 @@ static struct  hv_driver netvsc_drv = {
 	},
 };
 
-/* Set VF's namespace same as the synthetic NIC */
-static void netvsc_event_set_vf_ns(struct net_device *ndev)
-{
-	struct net_device_context *ndev_ctx = netdev_priv(ndev);
-	struct net_device *vf_netdev;
-	int ret;
-
-	vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
-	if (!vf_netdev)
-		return;
-
-	if (!net_eq(dev_net(ndev), dev_net(vf_netdev))) {
-		ret = dev_change_net_namespace(vf_netdev, dev_net(ndev),
-					       "eth%d");
-		if (ret)
-			netdev_err(vf_netdev,
-				   "Cannot move to same namespace as %s: %d\n",
-				   ndev->name, ret);
-		else
-			netdev_info(vf_netdev,
-				    "Moved VF to namespace with: %s\n",
-				    ndev->name);
-	}
-}
-
 /*
  * On Hyper-V, every VF interface is matched with a corresponding
  * synthetic interface. The synthetic interface is presented first
@@ -2809,11 +2797,6 @@ static int netvsc_netdev_event(struct notifier_block *this,
 	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
 	int ret = 0;
 
-	if (event_dev->netdev_ops == &device_ops && event == NETDEV_REGISTER) {
-		netvsc_event_set_vf_ns(event_dev);
-		return NOTIFY_DONE;
-	}
-
 	ret = check_dev_is_matching_vf(event_dev);
 	if (ret != 0)
 		return NOTIFY_DONE;
-- 
2.34.1

Re: [PATCH net] hv_netvsc: Switch VF namespace in netvsc_open instead

[Jakub Kicinski]

On Fri, 11 Jul 2025 13:57:10 -0700 Haiyang Zhang wrote:
> 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:

Are you saying that when netns is dismantled both devices are listed
for moving back to default, but the netvsc_event_set_vf_ns() logic
tries to undo the move / move the VF before the netns dismantle loop
got to it?

This needs a better fix, moving on open is way too hacky. 
Perhaps we should start with reverting 4c262801ea60 and then trying
to implement it in a more robust way?
-- 
pw-bot: cr

RE: [EXTERNAL] Re: [PATCH net] hv_netvsc: Switch VF namespace in netvsc_open instead

[Haiyang Zhang]

> -----Original Message-----
> From: Jakub Kicinski <kuba@kernel.org>
> Sent: Monday, July 14, 2025 9:29 PM
> To: Haiyang Zhang <haiyangz@linux.microsoft.com>
> Cc: linux-hyperv@vger.kernel.org; netdev@vger.kernel.org; Haiyang Zhang
> <haiyangz@microsoft.com>; KY Srinivasan <kys@microsoft.com>;
> wei.liu@kernel.org; Dexuan Cui <decui@microsoft.com>; edumazet@google.com;
> pabeni@redhat.com; stephen@networkplumber.org; davem@davemloft.net; linux-
> kernel@vger.kernel.org; stable@vger.kernel.org
> Subject: [EXTERNAL] Re: [PATCH net] hv_netvsc: Switch VF namespace in
> netvsc_open instead
> 
> On Fri, 11 Jul 2025 13:57:10 -0700 Haiyang Zhang wrote:
> > 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:
> 
> Are you saying that when netns is dismantled both devices are listed
> for moving back to default, but the netvsc_event_set_vf_ns() logic
> tries to undo the move / move the VF before the netns dismantle loop
> got to it?

netvsc_event_set_vf_ns() moves the VF to default ns before the netns 
dismantle loop got to it, and causes the Null prt error.

> This needs a better fix, moving on open is way too hacky.
> Perhaps we should start with reverting 4c262801ea60 and then trying
> to implement it in a more robust way?

This patch reverts the 4c262801ea60, and moves the logic to netvsc_open().

I was thinking some other ways too... But seems I couldn't find a way
to know it's in the for_each_netdev_safe loop, and to skip moving the 
VF in netvsc_event_set_vf_ns() this case.

Thanks,
- Haiyang