Bug 13312

Summary:	at76c50x-usb mutex deadlock
Product:	Drivers	Reporter:	karlrelton000+ubuntu
Component:	network-wireless	Assignee:	drivers_network-wireless (drivers_network-wireless)
Status:	CLOSED CODE_FIX
Severity:	normal	CC:	kvalo, linville
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	2.6.30-rc5	Subsystem:
Regression:	No	Bisected commit-id:
Attachments:	0001-at76c50x-usb-avoid-mutex-deadlock-in-at76_dwork_hw_.patch

Description karlrelton000+ubuntu 2009-05-14 20:54:53 UTC

at76_dwork_hw_scan() does a mutex_lock and then calls ieee80211_scan_completed(). This in turn calls at76_config() which then tries to do the same mutex_lock and thus the driver goes into deadlock.

I believe the solution would be for at76_dwork_hw_scan() to unlock the mutex before calling ieee80211_scan_completed(). I've tried this with my card, and it does indeed avoid the lockup - though I have yet to get the card working properly with this driver.

Comment 1 Andrew Morton 2009-05-28 07:49:30 UTC

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Thu, 14 May 2009 20:54:54 GMT bugzilla-daemon@bugzilla.kernel.org wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=13312
> 
>            Summary: at76c50x-usb mutex deadlock
>            Product: Drivers
>            Version: 2.5
>     Kernel Version: 2.6.30-rc5
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: network-wireless
>         AssignedTo: drivers_network-wireless@kernel-bugs.osdl.org
>         ReportedBy: karllinuxtest.relton@ntlworld.com
>                 CC: kalle.valo@iki.fi
>         Regression: No
> 
> 
> at76_dwork_hw_scan() does a mutex_lock and then calls
> ieee80211_scan_completed(). This in turn calls at76_config() which then tries
> to do the same mutex_lock and thus the driver goes into deadlock.
> 
> I believe the solution would be for at76_dwork_hw_scan() to unlock the mutex
> before calling ieee80211_scan_completed(). I've tried this with my card, and
> it
> does indeed avoid the lockup - though I have yet to get the card working
> properly with this driver.
> 

umm, is anyone looking at
drivers_network-wireless@kernel-bugs.osdl.org?  This one seems a bit of
a no-brainer?

Comment 2 John W. Linville 2009-05-28 09:47:11 UTC

Created attachment 21599 [details]
0001-at76c50x-usb-avoid-mutex-deadlock-in-at76_dwork_hw_.patch

Would you mind trying this patch?

Comment 3 karlrelton000+ubuntu 2009-05-31 17:53:27 UTC

The patch does resolve the mutex lockup.

Comment 4 John W. Linville 2010-03-05 18:40:31 UTC

commit 21a4cc00e8e67edcfc1bdb9af6d370ed1226eb86
Author: John W. Linville <linville@tuxdriver.com>
Date:   Thu May 28 11:39:02 2009 +0200

    at76c50x-usb: avoid mutex deadlock in at76_dwork_hw_scan
    
    http://bugzilla.kernel.org/show_bug.cgi?id=13312
    
    at76_dwork_hw_scan holds a mutex while calling ieee80211_scan_completed,
    which then calls at76_config which needs the same mutex.  This reworks
    the ordering to not hold the lock while calling ieee80211_scan_completed.
    
    Signed-off-by: John W. Linville <linville@tuxdriver.com>