[Bug 208860] [net80211]: ieee80211_waitfor_parent() will hang forever if something is enqueued into the taskqueue

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=208860

            Bug ID: 208860
           Summary: [net80211]: ieee80211_waitfor_parent() will hang
                    forever if something is enqueued into the taskqueue
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: wireless
          Assignee: freebsd-wireless at FreeBSD.org
          Reporter: avos at freebsd.org

Manual tracing (wlan0 and wlan2 are monitor mode vaps on wpi0):

wlan0:
wlan0: ieee80211_ioctl: before ieee80211_start_locked()
wlan0: start running, 0 vaps running
wlan0: ieee80211_start_locked: up parent wpi0
wlan0: ieee80211_ioctl: before ieee80211_waitfor_parent(), wait=1
wlan0: ieee80211_waitfor_parent: before taskqueue_block()
wlan0: ieee80211_waitfor_parent: ieee80211_draintask(ic, &ic->ic_parent_task);
<<< hangs here

wlan2:
wlan2: ieee80211_ioctl: before ieee80211_start_locked()
wlan2: start running, 1 vaps running
wlan2: ieee80211_new_state_locked: INIT -> RUN (nrunning 0 nscanning 0)
wlan2: ieee80211_ioctl: before ieee80211_waitfor_parent(), wait=0
<<< no progress too

Since the manpage for taskqueue(9) states

> The taskqueue_block() function blocks the taskqueue.  It prevents any
> enqueued but  not running tasks from being executed.

and

> Note that if taskqueue_drain() is called on a task that is enqueued on a
> taskqueue that is blocked by taskqueue_block(), then taskqueue_drain()
> can not return until the taskqueue is unblocked.

this function will never work as expected (probably, it should set a flag for
ieee80211_runtask() + call taskqueue_drain_all() instead).

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