Re: [PATCH net-next v6 4/9] vsock/loopback: add netns support

On Tue, Sep 16, 2025 at 04:43:48PM -0700, Bobby Eshleman wrote:

From: Bobby Eshleman bobbyeshleman@meta.com

Add NS support to vsock loopback. Sockets in a global mode netns communicate with each other, regardless of namespace. Sockets in a local mode netns may only communicate with other sockets within the same namespace.

Use pernet_ops to install a vsock_loopback for every namespace that is created (to be used if local mode is enabled).

Retroactively call init/exit on every namespace when the vsock_loopback module is loaded in order to initialize the per-ns device.

Signed-off-by: Bobby Eshleman bobbyeshleman@meta.com

---

Changes in v6:

• init pernet ops for vsock_loopback module
• vsock_loopback: add space in struct to clarify lock protection
• do proper cleanup/unregister on vsock_loopback_exit()
• vsock_loopback: use virtio_vsock_skb_net()

Changes in v5:

• add callbacks code to avoid reverse dependency
• add logic for handling vsock_loopback setup for already existing

namespaces

include/net/af_vsock.h | 1 + include/net/netns/vsock.h | 6 +++ net/vmw_vsock/vsock_loopback.c | 98 ++++++++++++++++++++++++++++++++++++++---- 3 files changed, 97 insertions(+), 8 deletions(-)

Just tried to boot a Fedora 42 VM with these patches applied on top of master, commit 4ff71af020ae ("Merge tag 'net-6.17-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net")

And during the boot I have this:

[ 5.117627] systemd[1]: Detected virtualization kvm. [ 5.117650] systemd[1]: Detected architecture x86-64. [ 5.141282] systemd[1]: bpf-restrict-fs: BPF LSM hook not enabled in the kernel, BPF LSM not supported. [ 5.317525] NET: Registered PF_VSOCK protocol family [ 5.320496] Guest personality initialized and is inactive [ 5.320960] VMCI host device registered (name=vmci, major=10, minor=259) [ 5.320965] Initialized host personality [ 5.465051] ------------[ cut here ]------------ [ 5.465068] WARNING: CPU: 1 PID: 297 at net/vmw_vsock/vsock_loopback.c:164 vsock_loopback_init_net+0x4a/0x60 [vsock_loopback] [ 5.465081] Modules linked in: vsock_loopback(+) vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vmw_vmci vsock virtio_rng rng_core [ 5.465115] CPU: 1 UID: 0 PID: 297 Comm: modprobe Not tainted 6.17.0-rc7-ste-00128-gcb48f49ce0ac #40 PREEMPT(none) [ 5.465123] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-5.fc42 04/01/2014 [ 5.465127] RIP: 0010:vsock_loopback_init_net+0x4a/0x60 [vsock_loopback] [ 5.465134] Code: 48 8b 3d b9 43 22 c2 e8 e4 e9 53 c1 48 89 83 e8 0e 00 00 48 85 c0 74 1b 48 89 c7 e8 f0 fe ff ff 48 8b 5d f8 c9 c3 cc cc cc cc <0f> 0b 31 c0 c3 cc cc cc cc b8 f4 ff ff ff eb e6 66 0f 1f 44 00 00 [ 5.465140] RSP: 0018:ffffc900002afb48 EFLAGS: 00010286 [ 5.465147] RAX: ffffffff836c8798 RBX: 0000000000000000 RCX: ffffffffc0015056 [ 5.465151] RDX: 0000000000000000 RSI: 0000000000000100 RDI: ffffffff836c8700 [ 5.465155] RBP: ffffc900002afb60 R08: ffff88800c0bd378 R09: 00000000f4197968 [ 5.465159] R10: 0000000000000200 R11: 0000000003ad91eb R12: ffffffff836c8700 [ 5.465163] R13: ffffffffc023f240 R14: ffffffffc0015010 R15: 0000000000000000 [ 5.465172] FS: 00007f2f6c3e1b80(0000) GS:ffff8880fb4d2000(0000) knlGS:0000000000000000 [ 5.465192] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5.465196] CR2: 00007f27ae2e7000 CR3: 000000000b436001 CR4: 0000000000770ef0 [ 5.465200] PKRU: 55555554 [ 5.465203] Call Trace: [ 5.465206] <TASK> [ 5.465210] ? vsock_loopback_init+0x6c/0xff0 [vsock_loopback] [ 5.465217] do_one_initcall+0x73/0x2d0 [ 5.465233] do_init_module+0x65/0x210 [ 5.465243] load_module+0x1a6e/0x1cf0 [ 5.465256] init_module_from_file+0x92/0xd0 [ 5.465260] ? init_module_from_file+0x92/0xd0 [ 5.465269] idempotent_init_module+0x12d/0x340 [ 5.465278] __x64_sys_finit_module+0x60/0xb0 [ 5.465284] x64_sys_call+0x18a0/0x1d80 [ 5.465291] do_syscall_64+0x73/0x320 [ 5.465302] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 5.465307] RIP: 0033:0x7f2f6c4d60cd [ 5.465312] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 03 4d 0f 00 f7 d8 64 89 01 48 [ 5.465317] RSP: 002b:00007ffe7166e7a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139 [ 5.465323] RAX: ffffffffffffffda RBX: 000055d75bab9e40 RCX: 00007f2f6c4d60cd [ 5.465326] RDX: 0000000000000000 RSI: 000055d75bab15ee RDI: 0000000000000005 [ 5.465330] RBP: 00007ffe7166e860 R08: 0000000000000000 R09: 000055d75baba520 [ 5.465333] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000040000 [ 5.465336] R13: 000055d75baba940 R14: 000055d75bab15ee R15: 0000000000000000 [ 5.465391] </TASK> [ 5.465395] irq event stamp: 15179 [ 5.465399] hardirqs last enabled at (15185): [<ffffffff81350e9e>] __up_console_sem+0x5e/0x80 [ 5.465407] hardirqs last disabled at (15190): [<ffffffff81350e83>] __up_console_sem+0x43/0x80 [ 5.465411] softirqs last enabled at (15172): [<ffffffff812d2e21>] irq_exit_rcu+0x61/0xb0 [ 5.465419] softirqs last disabled at (15165): [<ffffffff812d2e21>] irq_exit_rcu+0x61/0xb0 [ 5.465425] ---[ end trace 0000000000000000 ]---

And could be related to a potential issue I see in vsock_loopback_init() (see comment later).

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index 628e35ae9d00..5180b7dbb6d6 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -320,4 +320,5 @@ static inline bool vsock_net_check_mode(struct vsock_sock *vsk, struct net *net,

return orig_net_mode == VSOCK_NET_MODE_GLOBAL && vsk->orig_net_mode == VSOCK_NET_MODE_GLOBAL; }

#endif /* __AF_VSOCK_H__ */ diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h index d4593c0b8dc4..a32d546793a2 100644 --- a/include/net/netns/vsock.h +++ b/include/net/netns/vsock.h @@ -9,6 +9,8 @@ enum vsock_net_mode { VSOCK_NET_MODE_LOCAL, };

+struct vsock_loopback;

struct netns_vsock { struct ctl_table_header *vsock_hdr; spinlock_t lock; @@ -16,5 +18,9 @@ struct netns_vsock { /* protected by lock */ enum vsock_net_mode mode; bool written;

+#if IS_ENABLED(CONFIG_VSOCKETS_LOOPBACK)

• struct vsock_loopback *loopback;

+#endif

Honestly, I don't really like having something specific to a transport here. Could we have something more generic to allow a generic transport to register private data?

(It's not a strong opinion; we can resolve it in the future when we will have support for more transports if it's complicated)

}; #endif /* __NET_NET_NAMESPACE_VSOCK_H */ diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c index 1b2fab73e0d0..134e0619de07 100644 --- a/net/vmw_vsock/vsock_loopback.c +++ b/net/vmw_vsock/vsock_loopback.c @@ -28,8 +28,16 @@ static u32 vsock_loopback_get_local_cid(void)

static int vsock_loopback_send_pkt(struct sk_buff *skb) {

• struct vsock_loopback *vsock = &the_vsock_loopback;

• struct vsock_loopback *vsock; int len = skb->len;
• struct net *net;
• net = virtio_vsock_skb_net(skb);
• if (net && net->vsock.mode == VSOCK_NET_MODE_LOCAL)

Can `net` be NULL ? If not, I'd print a warning or return an error.

• vsock = net->vsock.loopback;
  

• else

• vsock = &the_vsock_loopback;
  
  

  virtio_vsock_skb_queue_tail(&vsock->pkt_queue, skb); queue_work(vsock->workqueue, &vsock->pkt_work);

@@ -134,27 +142,99 @@ static void vsock_loopback_work(struct work_struct *work) } }

-static int __init vsock_loopback_init(void) +static int vsock_loopback_init_vsock(struct vsock_loopback *vsock) {

• struct vsock_loopback *vsock = &the_vsock_loopback;

• int ret;

• vsock->workqueue = alloc_workqueue("vsock-loopback", 0, 0); if (!vsock->workqueue) return -ENOMEM;

  skb_queue_head_init(&vsock->pkt_queue); INIT_WORK(&vsock->pkt_work, vsock_loopback_work);

nit: leave a blank line here.

• return 0;

+}

+static void vsock_loopback_deinit_vsock(struct vsock_loopback *vsock) +{

• if (vsock->workqueue)

• destroy_workqueue(vsock->workqueue);
  

+}

+static int vsock_loopback_init_net(struct net *net) +{

• if (WARN_ON_ONCE(net->vsock.loopback))

• return 0;
  

• net->vsock.loopback = kmalloc(sizeof(*net->vsock.loopback), GFP_KERNEL);
• if (!net->vsock.loopback)

• return -ENOMEM;
  

• return vsock_loopback_init_vsock(net->vsock.loopback);

+}

+static void vsock_loopback_exit_net(struct net *net) +{

• if (net->vsock.loopback) {

• vsock_loopback_deinit_vsock(net->vsock.loopback);
  

• kfree(net->vsock.loopback);
  

• net->vsock.loopback = NULL;
  

• }

+}

+static void vsock_loopback_deinit_all(void) +{

• struct net *net;
• down_read(&net_rwsem);
• for_each_net(net)

• vsock_loopback_exit_net(net);
  

• up_read(&net_rwsem);

+}

+static struct pernet_operations vsock_loopback_net_ops = {

• .init = vsock_loopback_init_net,
• .exit = vsock_loopback_exit_net,

+};

+static int __init vsock_loopback_init(void) +{

• struct vsock_loopback *vsock = &the_vsock_loopback;
• struct net *net;
• int ret;
• ret = vsock_loopback_init_vsock(vsock);
• if (ret < 0)

• return ret;
  

• ret = register_pernet_subsys(&vsock_loopback_net_ops);
• if (ret < 0)

• goto out_deinit_vsock;
  

• /* call callbacks on any net previously created */
• down_read(&net_rwsem);

This could be related to the trace I posted on top.

Should we move the register_pernet_subsys() in the section protected by `net_rwsem`?

Because if a net is created just after this code returns from `register_pernet_subsys()`, we are going to call vsock_loopback_init_net() again here in this loop, no?

• for_each_net(net) {

• ret = vsock_loopback_init_net(net);
  

• if (ret < 0)
  

• 	break;
  

• }
• up_read(&net_rwsem);
• /* undo any initializations that succeeded */

useless comment.

• if (ret < 0)

• goto out_deinit_pernet_vsock;
  

I'd move in the for block calling `up_read` before the goto, but not a strong opinion.

ret = vsock_core_register(&loopback_transport.transport, VSOCK_TRANSPORT_F_LOCAL); if (ret)

• goto out_wq;
  

• goto out_deinit_pernet_vsock;
  

• return 0;

-out_wq:

• destroy_workqueue(vsock->workqueue);

+out_deinit_pernet_vsock:

• vsock_loopback_deinit_all();
• unregister_pernet_subsys(&vsock_loopback_net_ops);

What happen if a net is created after vsock_loopback_deinit_all()? Should we do the opposite? Or the unregister_pernet_subsys() should be called in the `net_rwsem` section?

+out_deinit_vsock:

• vsock_loopback_deinit_vsock(vsock); return ret;

}

@@ -164,6 +244,8 @@ static void __exit vsock_loopback_exit(void)

vsock_core_unregister(&loopback_transport.transport);

• vsock_loopback_deinit_all();

Should we call also `unregister_pernet_subsys()` ? Or in some way is automatically called since we are exiting?

Thanks, Stefano

flush_work(&vsock->pkt_work);

virtio_vsock_skb_queue_purge(&vsock->pkt_queue);

destroy_workqueue(vsock->workqueue);

What about replacing this with `vsock_loopback_deinit_vsock()` ?

Just to follow what we do in `vsock_loopback_init`.

Thanks, Stefano