hv_netvsc: Fix race condition between netvsc_probe and netvsc_remove

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]