In the Linux kernel, the following vulnerability has been resolved:

hv_netvsc: Fix race condition between netvsc_probe and netvsc_remove

In commit ac5047671758 ("hv_netvsc: Disable NAPI before closing the
VMBus channel"), napi_disable was getting called for all channels,
including all subchannels without confirming if they are enabled or not.

This caused hv_netvsc getting hung at napi_disable, when netvsc_probe()
has finished running but nvdev->subchan_work has not started yet.
netvsc_subchan_work() -> rndis_set_subchannel() has not created the
sub-channels and because of that netvsc_sc_open() is not running.
netvsc_remove() calls cancel_work_sync(&nvdev->subchan_work), for which
netvsc_subchan_work did not run.

netif_napi_add() sets the bit NAPI_STATE_SCHED because it ensures NAPI
cannot be scheduled. Then netvsc_sc_open() -> napi_enable will clear the
NAPIF_STATE_SCHED bit, so it can be scheduled. napi_disable() does the
opposite.

Now during netvsc_device_remove(), when napi_disable is called for those
subchannels, napi_disable gets stuck on infinite msleep.

This fix addresses this problem by ensuring that napi_disable() is not
getting called for non-enabled NAPI struct.
But netif_napi_del() is still necessary for these non-enabled NAPI struct
for cleanup purpose.

Call trace:
[  654.559417] task:modprobe        state:D stack:    0 pid: 2321 ppid:  1091 flags:0x00004002
[  654.568030] Call Trace:
[  654.571221]  <TASK>
[  654.573790]  __schedule+0x2d6/0x960
[  654.577733]  schedule+0x69/0xf0
[  654.581214]  schedule_timeout+0x87/0x140
[  654.585463]  ? __bpf_trace_tick_stop+0x20/0x20
[  654.590291]  msleep+0x2d/0x40
[  654.593625]  napi_disable+0x2b/0x80
[  654.597437]  netvsc_device_remove+0x8a/0x1f0 [hv_netvsc]
[  654.603935]  rndis_filter_device_remove+0x194/0x1c0 [hv_netvsc]
[  654.611101]  ? do_wait_intr+0xb0/0xb0
[  654.615753]  netvsc_remove+0x7c/0x120 [hv_netvsc]
[  654.621675]  vmbus_remove+0x27/0x40 [hv_vmbus]

kernel.org https://git.kernel.org/stable/c/0e8875de9dad12805ff66e92cd5edea6a421f1cd [No types assigned]

kernel.org https://git.kernel.org/stable/c/22a77c0f5b8233237731df3288d067af51a2fd7b [No types assigned]

kernel.org https://git.kernel.org/stable/c/48a8ccccffbae10c91d31fc872db5c31aba07518 [No types assigned]

kernel.org https://git.kernel.org/stable/c/7656372ae190e54e8c8cf1039725a5ea59fdf84a [No types assigned]

kernel.org https://git.kernel.org/stable/c/9ec807e7b6f5fcf9499f3baa69f254bb239a847f [No types assigned]

kernel.org https://git.kernel.org/stable/c/e0526ec5360a48ad3ab2e26e802b0532302a7e11 [No types assigned]