Re: BUG: unable to handle kernel NULL pointer dereference at0000000000000040

[nirinA raseliarison]

on Sat, 15 Jun 2013 11:08:47 +0300, Ming Lei <ming.lei@xxxxxxxxxxxxx>  
wrote:

> On Sat, Jun 15, 2013 at 2:30 PM, Guenter Roeck <linux@xxxxxxxxxxxx>  
> wrote:
> > On Sat, Jun 15, 2013 at 10:32:14AM +0800, Ming Lei wrote:
> > > On Sat, Jun 15, 2013 at 1:07 AM, nirinA raseliarison
> > > <nirina.raseliarison@xxxxxxxxx> wrote:
> > >
> > > > patch applied and no longer have the bug message when i
> > > > reboot and wake up the ethernet controller.
> > >
> > > I am wondering if Guenter's patch can fix the race really, but I'd  
> > > like to
> > > see Guenter's explanation on his patch.
> > >
> > > The race should be caused by below:
> > >
> > > - request timeout triggered by internal timer
> > >
> > > - user space aborts the requests before the line in  
> > > _request_firmware_load()
> > >
> > >              fw_priv->buf = NULL
> > >
> > > which is run in timeout path
> > >
> > > - then the abort() called from firmware_loading_store() may use a  
> > > freed fw buf
> > > since the timeout path will free the fw buffer.
> > >
> > > Considered clearing 'fw_priv->buf' in _request_firmware_load()() isn't  
> > > protected
> > > by fw_lock now, so Guenter's patch can't avoid the race entirely.
> > I agree; my patch only protects one specific path, and was based on the
> > observation that access to fw_priv->buf is protected elsewhwere in the  
> > code.
> > My suspicion was that fw_priv->buf was freed while waiting for the  
> > mutex in
> > firmware_loading_store().
> >
> > Your patch is more comprehensive.
>
> OK, thanks for your reply.
>
> I will post out one version for merge, and this one moves the
> "fw_priv->buf = NULL;" into fw_load_abort() for simplifying change.

this is just to let you know that i've tested Ming Lei's latest patch.
thank you very much for the fix and the explanation.

--
nirinA
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/