svn commit: r343213 - in head/sys: net80211 sys

[Bjoern A. Zeeb]

On 20 Jan 2019, at 13:39, Andriy Voskoboinyk wrote:

> Author: avos
> Date: Sun Jan 20 13:39:18 2019
> New Revision: 343213
> URL: https://svnweb.freebsd.org/changeset/base/343213
>
> Log:
>   net80211: resolve ioctl <-> detach race for ieee80211com structure
>
>   Since r287197 ieee80211com is a part of drivers softc; as a result,
>   after detach all pointers to it (iv_ic, ni_ic) are invalid. Most
>   possible users (tasks, interrupt handlers) are blocked / removed
>   when device is stopped; however, ioctl handlers were not tracked
>   and may crash if ieee80211com structure is accessed.
>
>   Since ieee80211com pointer access from ieee80211vap structure is not
>   protected by lock (constant after interface creation) and used in
>   many other places just use reference counting for ioctl handlers;
>   on detach set 'detached' flag and wait until reference counter goes 
> to 0.

So how do any cloned interfaces do this (wifi or non-wifi)?  Is this a 
more general problem or are some wifi drivers just not exactly careful 
with the order they take things down?

On another note, why would refcount(9) not be sufficient?  I didn’t 
really like the MC() macros and the hand crafted state machine for a 
refcount when scrolling through.

/bz