Describe CVE-2021-47349.
What is CVE-2021-47349?
In the Linux kernel, the following vulnerability has been resolved:

mwifiex: bring down link before deleting interface

We can deadlock when rmmod'ing the driver or going through firmware
reset, because the cfg80211_unregister_wdev() has to bring down the link
for us, ... which then grab the same wiphy lock.

nl80211_del_interface() already handles a very similar case, with a nice
description:

        /*
         * We hold RTNL, so this is safe, without RTNL opencount cannot
         * reach 0, and thus the rdev cannot be deleted.
         *
         * We need to do it for the dev_close(), since that will call
         * the netdev notifiers, and we need to acquire the mutex there
         * but don't know if we get there from here or from some other
         * place (e.g. "ip link set ... down").
         */
        mutex_unlock(&rdev->wiphy.mtx);
...

Do similarly for mwifiex teardown, by ensuring we bring the link down
first.

Sample deadlock trace:

[  247.103516] INFO: task rmmod:2119 blocked for more than 123 seconds.
[  247.110630]       Not tainted 5.12.4 #5
[  247.115796] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  247.124557] task:rmmod           state:D stack:    0 pid: 2119 ppid:  2114 flags:0x00400208
[  247.133905] Call trace:
[  247.136644]  __switch_to+0x130/0x170
[  247.140643]  __schedule+0x714/0xa0c
[  247.144548]  schedule_preempt_disabled+0x88/0xf4
[  247.149714]  __mutex_lock_common+0x43c/0x750
[  247.154496]  mutex_lock_nested+0x5c/0x68
[  247.158884]  cfg80211_netdev_notifier_call+0x280/0x4e0 [cfg80211]
[  247.165769]  raw_notifier_call_chain+0x4c/0x78
[  247.170742]  call_netdevice_notifiers_info+0x68/0xa4
[  247.176305]  __dev_close_many+0x7c/0x138
[  247.180693]  dev_close_many+0x7c/0x10c
[  247.184893]  unregister_netdevice_many+0xfc/0x654
[  247.190158]  unregister_netdevice_queue+0xb4/0xe0
[  247.195424]  _cfg80211_unregister_wdev+0xa4/0x204 [cfg80211]
[  247.201816]  cfg80211_unregister_wdev+0x20/0x2c [cfg80211]
[  247.208016]  mwifiex_del_virtual_intf+0xc8/0x188 [mwifiex]
[  247.214174]  mwifiex_uninit_sw+0x158/0x1b0 [mwifiex]
[  247.219747]  mwifiex_remove_card+0x38/0xa0 [mwifiex]
[  247.225316]  mwifiex_pcie_remove+0xd0/0xe0 [mwifiex_pcie]
[  247.231451]  pci_device_remove+0x50/0xe0
[  247.235849]  device_release_driver_internal+0x110/0x1b0
[  247.241701]  driver_detach+0x5c/0x9c
[  247.245704]  bus_remove_driver+0x84/0xb8
[  247.250095]  driver_unregister+0x3c/0x60
[  247.254486]  pci_unregister_driver+0x2c/0x90
[  247.259267]  cleanup_module+0x18/0xcdc [mwifiex_pcie].