On Fri, Sep 03, 2021 at 12:39:49AM +0300, Vladimir Oltean wrote: > On Thu, Sep 02, 2021 at 10:33:03PM +0100, Russell King (Oracle) wrote: > > That's probably an unreliable indicator. DPAA2 has weirdness in the > > way it can dynamically create and destroy network interfaces, which > > does lead to problems with the rtnl lock. I've been carrying a patch > > from NXP for this for almost two years now, which NXP still haven't > > submitted: > > > > http://git.armlinux.org.uk/cgit/linux-arm.git/commit/?h=cex7&id=a600f2ee50223e9bcdcf86b65b4c427c0fd425a4 > > > > ... and I've no idea why that patch never made mainline. I need it > > to avoid the stated deadlock on SolidRun Honeycomb platforms when > > creating additional network interfaces for the SFP cages in userspace. > > Ah, nice, I've copied that broken logic for the dpaa2-switch too: > https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d52ef12f7d6c016f3b249db95af33f725e3dd065 > > So why don't you send the patch? I can send it too if you want to, one > for the switch and one for the DPNI driver. Sorry, I mis-stated. NXP did submit that exact patch, but it's actually incorrect for the reason I stated when it was sent: https://patchwork.ozlabs.org/project/netdev/patch/1574363727-5437-2-git-send-email-ioana.ciornei@xxxxxxx/ I did miss the rtnl_lock() around phylink_disconnect_phy() in the description of the race, which goes someway towards hiding it, but there is still a race between phylink_destroy() and another thread calling dpaa2_eth_get_link_ksettings(), and priv->mac being freed: static int dpaa2_eth_get_link_ksettings(struct net_device *net_dev, struct ethtool_link_ksettings *link_settings) { struct dpaa2_eth_priv *priv = netdev_priv(net_dev); if (dpaa2_eth_is_type_phy(priv)) return phylink_ethtool_ksettings_get(priv->mac->phylink, link_settings); which dereferences priv->mac and priv->mac->phylink, vs: static irqreturn_t dpni_irq0_handler_thread(int irq_num, void *arg) { ... if (status & DPNI_IRQ_EVENT_ENDPOINT_CHANGED) { dpaa2_eth_set_mac_addr(netdev_priv(net_dev)); dpaa2_eth_update_tx_fqids(priv); if (dpaa2_eth_has_mac(priv)) dpaa2_eth_disconnect_mac(priv); else dpaa2_eth_connect_mac(priv); } static void dpaa2_eth_disconnect_mac(struct dpaa2_eth_priv *priv) { if (dpaa2_eth_is_type_phy(priv)) dpaa2_mac_disconnect(priv->mac); if (!dpaa2_eth_has_mac(priv)) return; dpaa2_mac_close(priv->mac); kfree(priv->mac); <== potential use after free bug by priv->mac = NULL; <== dpaa2_eth_get_link_ksettings() } void dpaa2_mac_disconnect(struct dpaa2_mac *mac) { if (!mac->phylink) return; phylink_disconnect_phy(mac->phylink); phylink_destroy(mac->phylink); <== another use-after-free bug via dpaa2_eth_get_link_ksettings() dpaa2_pcs_destroy(mac); } Note that phylink_destroy() is documented as: * Note: the rtnl lock must not be held when calling this function. because it calls sfp_bus_del_upstream(), which will take the rtnl lock itself. An alternative solution would be to remove the rtnl locking from sfp_bus_del_upstream(), but then force _everyone_ to take the rtnl lock before calling phylink_destroy() - meaning a larger block of code ends up executing under the lock than is really necessary. However, as I stated in my review of the patch "As I've already stated, the phylink is not designed to be created and destroyed on a published network device." That still remains true today, and it seems that the issue has never been fixed in DPAA2 despite having been pointed out. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
