Date:   Tue, 16 Apr 2019 10:33:05 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     Lorenzo Bianconi <lorenzo@kernel.org>, nbd@nbd.name,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH] mt76: usb: fix possible memory leak during suspend/resume
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On Apr 16, Stanislaw Gruszka wrote:
> On Tue, Apr 16, 2019 at 10:12:42AM +0200, Lorenzo Bianconi wrote:
> > > On Mon, Apr 15, 2019 at 05:04:06PM +0200, Lorenzo Bianconi wrote:
> > > > > On Sat, Apr 13, 2019 at 12:10:59PM +0200, Lorenzo Bianconi wrote:
> > > > > > > On Fri, Apr 12, 2019 at 06:27:48PM +0200, Lorenzo Bianconi wr=
ote:
> > > > > > > > > > On Fri, Apr 12, 2019 at 02:27:16PM +0200, Lorenzo Bianc=
oni wrote:
> > > > > > > > > > > Disable mt76u_tx_tasklet at the end of mt76u_stop_que=
ues in order to
> > > > > > > > > > > properly deallocate all pending skbs during suspend/r=
esume phase
> > > > > > > > > >=20
> > > > > > > > > > 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).
> > > > > > > > >=20
> > > > > > > > > Hi Stanislaw,
> > > > > > > > >=20
> > > > > > > > > I guess the right moment to deallocate the skbs is during=
 suspend since resume
> > > > > > > > > can happen in very far future
> > > > > > >=20
> > > > > > > Yes, it's better to free on suspend, but in practice does not=
 really matter since
> > > > > > > system is disabled till resume.
> > > > > > >=20
> > > > > > > > > > > Fixes: b40b15e1521f ("mt76: add usb support to mt76 l=
ayer")
> > > > > > > > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > > > > > > > > > ---
> > > > > > > > > > >  drivers/net/wireless/mediatek/mt76/usb.c | 4 ++--
> > > > > > > > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > > > > > >=20
> > > > > > > > > > > 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(struc=
t 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);
> > > > > > > > > >=20
> > > > > > > > > > If tasklet is scheduled and we disable it and never ena=
ble, we end up
> > > > > > > > > > with infinite loop in tasklet_action_common(). This pat=
ch make the
> > > > > > > > > > problem less reproducible since tasklet_disable() is mo=
ved after
> > > > > > > > > > usb_kill_urb() -> tasklet_schedule(), but it is still p=
ossible.
> > > > > > > > >=20
> > > > > > > > > I can see the point here. Maybe we can just run tasklet_k=
ill instead of
> > > > > > > > > tasklet_disable here (at least for tx one)
> > > > > > >=20
> > > > > > > I think you have right as tasklet_kill() will wait for schedu=
led tasklet .
> > > > > > > Originally in my patch (see below) I used wait_event as I tho=
ught
> > > > > > > tasklet_kill() may prevent scheduled tasklet to be executed (=
hence cause
> > > > > > > leak) but that seems to be not true.
> > > > > >=20
> > > > > > I agree with rx side (good catch!!), but on tx one I guess usb_=
kill_urb()
> > > > > > is already waiting for tx pending so we just need to use taskle=
t_kill
> > > > > > at the end of mt76u_stop_queues, in this way we will free pendi=
ng skbs during
> > > > > > suspend
> > > > >=20
> > > > > I looked more into that and there are some issues with this appro=
ach.
> > > > > tx_tasklet do mt76_txq_schedule() which can queue tx frames. Also=
 we
> > > > > do not free skb's that require status check and dev->usb.stat_wor=
k=20
> > > > > is already (correctly) stopped on mac80211.stop.=20
> > > >=20
> > > > right
> > > >=20
> > > > >=20
> > > > > I'll use wait_event(dev->tx_wait) on mac80211 stop to handle those
> > > > > issues correctly.
> > > >=20
> > > > ack
> > > >=20
> > > > >=20
> > > > > Stanislaw
> > > >=20
> > > > during device removal I guess we should also flush skbs in status q=
ueue, doing
> > > > something like (after commit 0b5f71304cd9 (mt76: introduce mt76_fre=
e_device
> > > > routine))
> > > >=20
> > > > diff --git a/drivers/net/wireless/mediatek/mt76/mt76x0/usb.c b/driv=
ers/net/wireless/mediatek/mt76/mt76x0/usb.c
> > > > index 1ef00e971cfa..d4d1eb003148 100644
> > > > --- a/drivers/net/wireless/mediatek/mt76/mt76x0/usb.c
> > > > +++ b/drivers/net/wireless/mediatek/mt76/mt76x0/usb.c
> > > > @@ -299,7 +299,7 @@ static void mt76x0_disconnect(struct usb_interf=
ace *usb_intf)
> > > >  	if (!initalized)
> > > >  		return;
> > > > =20
> > > > -	ieee80211_unregister_hw(dev->mt76.hw);
> > > > +	mt76_unregister_device(&dev->mt76);
> > >=20
> > > mt76_unregister_device() free mmio dma. I've added mt76_tx_status_che=
ck()
> > > on mt76u_stop_tx() routine instead.
> >=20
> > nope, after commit 0b5f71304cd98fb7b3b5b3a633e470bea979fe94
> > (https://github.com/nbd168/wireless/commit/0b5f71304cd98fb7b3b5b3a633e4=
70bea979fe94)
> > it can be used even for usb
>=20
> Ok, but as you pointed before 'right moment to deallocate the skbs is
> during suspend' so I still preffer to flush statuses there.
>=20

I agree

Lorenzo

> Stanislaw

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