Re: [PATCH] mt76: usb: fix possible memory leak during suspend/resume

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

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> > On Fri, Apr 12, 2019 at 02:27:16PM +0200, Lorenzo Bianconi wrote:
> > > Disable mt76u_tx_tasklet at the end of mt76u_stop_queues in order to
> > > properly deallocate all pending skbs during suspend/resume phase
> > 
> > On suspend/resume tx skb's are processed after tasklet_enable()
> > in resume callback. There is issue with device removal though
> > (during suspend or otherwise).
> 
> Hi Stanislaw,
> 
> I guess the right moment to deallocate the skbs is during suspend since resume
> can happen in very far future
> 
> > 
> > > Fixes: b40b15e1521f ("mt76: add usb support to mt76 layer")
> > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > ---
> > >  drivers/net/wireless/mediatek/mt76/usb.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> > > index a3acc070063a..575207133775 100644
> > > --- a/drivers/net/wireless/mediatek/mt76/usb.c
> > > +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> > > @@ -842,10 +842,10 @@ static void mt76u_stop_tx(struct mt76_dev *dev)
> > >  void mt76u_stop_queues(struct mt76_dev *dev)
> > >  {
> > >  	tasklet_disable(&dev->usb.rx_tasklet);
> > > -	tasklet_disable(&dev->usb.tx_tasklet);
> > > -
> > >  	mt76u_stop_rx(dev);
> > > +
> > >  	mt76u_stop_tx(dev);
> > > +	tasklet_disable(&dev->usb.tx_tasklet);
> > 
> > If tasklet is scheduled and we disable it and never enable, we end up
> > with infinite loop in tasklet_action_common(). This patch make the
> > problem less reproducible since tasklet_disable() is moved after
> > usb_kill_urb() -> tasklet_schedule(), but it is still possible.
> 
> I can see the point here. Maybe we can just run tasklet_kill instead of
> tasklet_disable here (at least for tx one)

I think it is enough even for rx side since usb_kill_urb() will wait the end of
mt76u_complete_rx() and tasklet_kill() will wait for the completion of
mt76u_rx_tasklet(). We will need to remove tasklet_enable in resume routines.

Regards,
Lorenzo

> 
> Regards,
> Lorenzo
> 
> > 
> > I comprehansive have fix for that, but giving it more testing.
> > Please drop this patch.
> > 
> > Stanislaw



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