Re: [PATCH V2 net] hv_netvsc: Fix race condition between netvsc_probe and netvsc_remove

[Simon Horman]

On Tue, Jan 30, 2024 at 11:35:51PM -0800, Souradeep Chakrabarti wrote:
> 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]
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: ac5047671758 ("hv_netvsc: Disable NAPI before closing the VMBus channel")
> Signed-off-by: Souradeep Chakrabarti <schakrabarti@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Reviewed-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>