Hello Vladimir!
On Wed, 2024-09-11 at 19:28 +0300, Vladimir Oltean wrote:
> On Wed, Sep 11, 2024 at 04:40:03PM +0200, A. Sverdlin wrote:
> > From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> >
> > dsa_switch_shutdown() doesn't bring down any ports, but only disconnects
> > slaves from master. Packets still come afterwards into master port and the
> > ports are being polled for link status. This leads to crashes:
> >
> > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> > CPU: 0 PID: 442 Comm: kworker/0:3 Tainted: G O 6.1.99+ #1
> > Workqueue: events_power_efficient phy_state_machine
> > pc : lan9303_mdio_phy_read
> > lr : lan9303_phy_read
> > Call trace:
> > lan9303_mdio_phy_read
> > lan9303_phy_read
> > dsa_slave_phy_read
> > __mdiobus_read
> > mdiobus_read
> > genphy_update_link
> > genphy_read_status
> > phy_check_link_status
> > phy_state_machine
> > process_one_work
> > worker_thread
> >
> > Call lan9303_remove() instead to really unregister all ports before zeroing
> > drvdata and dsa_ptr.
> >
> > Fixes: 0650bf52b31f ("net: dsa: be compatible with masters which unregister on shutdown")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> > ---
> > drivers/net/dsa/lan9303-core.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/dsa/lan9303-core.c b/drivers/net/dsa/lan9303-core.c
> > index 268949939636..ecd507355f51 100644
> > --- a/drivers/net/dsa/lan9303-core.c
> > +++ b/drivers/net/dsa/lan9303-core.c
> > @@ -1477,7 +1477,7 @@ EXPORT_SYMBOL(lan9303_remove);
> >
> > void lan9303_shutdown(struct lan9303 *chip)
> > {
> > - dsa_switch_shutdown(chip->ds);
> > + lan9303_remove(chip);
> > }
> > EXPORT_SYMBOL(lan9303_shutdown);
> >
> > --
> > 2.46.0
> >
>
> You've said here that a similar change still does not protect against
> packets received after shutdown:
> https://lore.kernel.org/netdev/c5e0e67400816d68e6bf90b4a999bfa28c59043b.camel@xxxxxxxxxxx/
>
> The difference between that and this is the extra lan9303_disable_processing_port()
> calls here. But while that does disable RX on switch ports, it still doesn't wait
> for pending RX frames to be processed. So the race is still open. No?
This patch addresses the race of zeroing drvdata in
static void lan9303_mdio_shutdown(struct mdio_device *mdiodev)
{
struct lan9303_mdio *sw_dev = dev_get_drvdata(&mdiodev->dev);
if (!sw_dev)
return;
lan9303_shutdown(&sw_dev->chip);
dev_set_drvdata(&mdiodev->dev, NULL);
}
versus
static int lan9303_mdio_phy_read(struct lan9303 *chip, int phy, int reg)
{
struct lan9303_mdio *sw_dev = dev_get_drvdata(chip->dev);
what you refer to is another race, zeroing of dsa_ptr in struct net_device versus
the whole network stack, which I addressed in
https://lore.kernel.org/netdev/20240910130321.337154-2-alexander.sverdlin@xxxxxxxxxxx/
--
Alexander Sverdlin
Siemens AG
www.siemens.com
