Re: [PATCH] Revert "net: linkwatch: add check for netdevice being present to linkwatch_do_dev"

[Saeed Mahameed <saeed@kernel.org>]

On Wed, 2020-09-23 at 13:49 +0200, Heiner Kallweit wrote:
> On 18.09.2020 19:58, Saeed Mahameed wrote:
> > On Tue, 2020-09-01 at 17:02 +0200, Geert Uytterhoeven wrote:
> > > This reverts commit 124eee3f6955f7aa19b9e6ff5c9b6d37cb3d1e2c.
> > > 
> > > Inami-san reported that this commit breaks bridge support in a
> > > Xen
> > > environment, and that reverting it fixes this.
> > > 
> > > During system resume, bridge ports are no longer enabled, as that
> > > relies
> > > on the receipt of the NETDEV_CHANGE notification.  This
> > > notification
> > > is
> > > not sent, as netdev_state_change() is no longer called.
> > > 
> > > Note that the condition this commit intended to fix never existed
> > > upstream, as the patch triggering it and referenced in the commit
> > > was
> > > never applied upstream.  Hence I can confirm s2ram on
> > > r8a73a4/ape6evm
> > > and sh73a0/kzm9g works fine before/after this revert.
> > > 
> > > Reported-by Gaku Inami <gaku.inami.xh@renesas.com>
> > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > > ---
> > >  net/core/link_watch.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/net/core/link_watch.c b/net/core/link_watch.c
> > > index 75431ca9300fb9c4..c24574493ecf95e6 100644
> > > --- a/net/core/link_watch.c
> > > +++ b/net/core/link_watch.c
> > > @@ -158,7 +158,7 @@ static void linkwatch_do_dev(struct
> > > net_device
> > > *dev)
> > >  	clear_bit(__LINK_STATE_LINKWATCH_PENDING, &dev->state);
> > >  
> > >  	rfc2863_policy(dev);
> > > -	if (dev->flags & IFF_UP && netif_device_present(dev)) {
> > > +	if (dev->flags & IFF_UP) {
> > 
> > So with your issue the devices is both IFF_UP and !present ? how so
> > ?
> > I think you should look into that.
> > 
> > I am ok with removing the "dev present" check from here just
> > because we
> > shouldn't  be expecting IFF_UP && !present .. such thing must be a
> > bug
> > somewhere else.
> > 
> > >  		if (netif_carrier_ok(dev))
> > >  			dev_activate(dev);
> > >  		else
> 
> In __dev_close_many() we call ndo_stop() whilst IFF_UP is still set.
> ndo_stop() may detach the device and bring down the PHY, resulting in
> an

Why would a driver detach the device on ndo_stop() ?
seems like this is the bug you need to be chasing ..
which driver is doing this ? 

> async link change event that calls dev_get_stats(). The latter call
> may
> have a problem if the device is detached. In a first place I'd
> consider
> such a case a network driver bug (ndo_get_stats/64 should check for
> device presence if depending on it).

Device drivers should avoid presence check as much as possible
especially in ndo, this check must be performed by the stack.

> The additional check in linkwatch_do_dev() was meant to protect from
> such
> driver issues.