nfc: nci: Fix race between rfkill and nci_unregister_device().
In the Linux kernel, the following vulnerability has been resolved: nfc: nci: Fix race between rfkill and nci_unregister_device(). syzbot reported the splat below [0] without a repro. It indicates that struct nci_dev.cmd_wq had been destroyed before nci_close_device() was called via rfkill. nci_dev.cmd_wq is only destroyed in nci_unregister_device(), which (I think) was called from virtual_ncidev_close() when syzbot close()d an fd of virtual_ncidev. The problem is that nci_unregister_device() destroys nci_dev.cmd_wq first and then calls nfc_unregister_device(), which removes the device from rfkill by rfkill_unregister(). So, the device