I need a little help in fixing `exclusive sleep mutex urtwn0_com_lock` in CURRENT

[Andriy Voskoboinyk]

Wed, 30 Mar 2016 12:30:48 +0300 було написано Aleksander Alekseev  
<mail at eax.me>:

> and then pull Wi-Fi adapter out of USB

Here (it's not the only driver which does detach incorrectly).


> Hello
>
> Today I found a way to crash CURRENT kernel. I'm a full-time *nix C
> developer but I never did kernel development before. I read "FreeBSD
> Device Drivers" and "FreeBSD Developer's Handbook" recently. Also I
> learned how to use DDB and KGDB. Discovered problem doesn't seem to be
> too complicated and I hope you could guide me a little bit through
> fixing it.
>
> I'm using TP-LINK TL-WN725N USB Wi-Fi adapter. When I do:
>
> sudo ifconfig wlan0 down
> sudo ifconfig wlan0 up
>
> ... and then pull Wi-Fi adapter out of USB kernel crashes like this:
>
> http://pastebin.com/raw/LkuE6Y7s
>
> It reproduces in 100% of cases.
>
> Here is a code that causes a problem (ieee80211_scan_sw.c:765):
>
> ```
> static void
> scan_end(struct ieee80211_scan_state *ss, int scandone)
> {
>         struct scan_state *ss_priv = SCAN_PRIVATE(ss);
>         struct ieee80211vap *vap = ss->ss_vap;
>         struct ieee80211com *ic = ss->ss_ic;
>
>         IEEE80211_LOCK_ASSERT(ic);
>
>         IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN, "%s: out\n",
>         __func__);
>
>         if (ss_priv->ss_iflags & ISCAN_ABORT) {
>                 scan_done(ss, scandone);
>                 return;
>         }
>
>         IEEE80211_UNLOCK(ic);
>         ic->ic_scan_end(ic);            /* notify driver */
>         IEEE80211_LOCK(ic); /* <--- HERE */
> ```
>
> So as I understand some code acquired a mutex and didn't release it.
> And naturally it has something to do with USB. Now how can I figure out
> what code acquired this lock? Best approach I can think of currently is
> to find all places where this lock is accessed and add a debug logging.
> But perhaps there is a better way?