Re: rt2x00: rt2800usb causing kernel panic /compat-wireless/

[Larry Finger <Larry.Finger@xxxxxxxxxxxx>]

On 05/18/2011 08:04 AM, Mohammed Shafi wrote:
> On Wed, May 18, 2011 at 6:21 PM, Gertjan van Wingerde
> <gwingerde@xxxxxxxxx>  wrote:
> > On 05/18/11 14:41, Mohammed Shafi wrote:
> > > On Wed, May 18, 2011 at 5:26 PM, Walter Goldens
> > > <goldenstranger@xxxxxxxxx>  wrote:
> > > > > > A very peculiar bug.
> > > > > >
> > > > > > With compat-wireless from 16.05 a nasty bug started to
> > > > > manifest itself. Right around association time, the
> > > > > rt2800usb causes kernel panic. The system freezes and the
> > > > > Caps Lock and Num Lock leds on the keyboard begin to flash.
> > > > >
> > > > > also ath9k, iwlagn.
> > > > >
> > > > > > Unfortunately there are no recoverable traces after
> > > > > the system failure to aid this bug report or to indicate its
> > > > > origin.
> > > > > > I believe it may somehow be related to Ubuntu's
> > > > > network-manager. If I turn off the network-manager service,
> > > > > I can go into monitor mode for example, but if
> > > > > network-manager is running and I plug my USB dongle, it
> > > > > starts to associate, a second or two later the system is in
> > > > > complete meltdown.
> > > > >
> > > > > same thing, monitor mode worked perfectly fine.
> > > > >
> > > > > > Nothing concrete, but a hunch is telling me this has
> > > > > something to do with the association mechanism of the
> > > > > rt2800usb. Compat-wireless from few days back exhibits no
> > > > > such foul play.
> > > > >
> > > > > yes just right at the association complete freeze.
> > > >
> > > > That's strange. I wonder what's the connection with this bug and network-manager. Because when I manually tried to associate, dmesg reported the association attempt timed out.
> > >
> > > no even when we use iw dev connect command we can see the panic.
> >
> > Yeah, I've seen this freeze as well using one of the later compat-wireless packages using just iw and wpa_supplicant to bring up the card. This is on all sorts of rt2x00 supported devices.
> >
> > However, I don't believe this to be an rt2x00-specific bug, as exactly the same rt2x00 sources inside a compat-wireless-2.6.39rc7 package do not produce the freeze.
> >
> > > some expert suspected that there is a chance of kfree_rcu in
> > > compat-wireless may have caused the problem
> >
> > That's where my suspicion is as well, but I didn't have the time to further investigate. Since my focus was on rt2x00 I used the compat-wireless-2.6.39rc7 package to test my patches. I only did a quick check, and the kfree_rcu compatibility fix that was done in compat-wireless did seem to match the kfree_rcu code is present in linux-next, but maybe there is an odd side-effect.
>
> I could not exactly remember this panic came just after kfree_rcu backported..

This problem also occurs with rtl8192se from compat-wireless. When it was 
reported to me, a photo of the console log was included (attached). The crash is 
a NULL pointer in rcu_do_batch.clone.19 (I think - the photo quality is minimal.).

Larry

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