On 5/13/26 2:02 PM, Aaron Conole wrote: > Hi Ilya, > > Ilya Maximets <[email protected]> writes: > >> Sashiko reports that it is technically possible that we got the device >> reference, but by the time we're linking it to the OVS datapath, it >> may be already in the process of being deleted. In this case if the >> notifier wins the race for RTNL, it will see that the device is not >> yet in the OVS datapath (ovs_netdev_get_vport() will fail in the >> dp_device_event()) and will do nothing. Then the ovs_netdev_link() >> will take the RTNL and link the unregistering device to OVS datapath. >> >> Eventually, netdev_wait_allrefs_any() will re-broadcast the event and >> the device will be properly detached, but it will take at least a >> second before that happens, so it's not something we should rely on. >> >> Let's avoid linking the non-registered device in the first place. >> >> Note: As per documentation, RTNL doesn't protect the reg_state, but >> it actually does for all the state transitions we care about here, >> so it should not be necessary to use READ_ONCE or taking the instance >> lock. We can still do that, but we have a few more places even in >> this file where the reg_state is accessed without those while under >> RTNL, and many more places like this across the kernel code, so it >> might make more sense to change all of them in a more centralized >> fashion in the future, if necessary. >> >> Fixes: ccb1352e76cf ("net: Add Open vSwitch kernel components.") >> Signed-off-by: Ilya Maximets <[email protected]> >> --- >> net/openvswitch/vport-netdev.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/net/openvswitch/vport-netdev.c b/net/openvswitch/vport-netdev.c >> index c42642075685d..de90d0541e172 100644 >> --- a/net/openvswitch/vport-netdev.c >> +++ b/net/openvswitch/vport-netdev.c >> @@ -83,6 +83,11 @@ struct vport *ovs_netdev_link(struct vport *vport, bool >> tunnel) >> } >> >> rtnl_lock(); > > As noted in your commit, this shouldn't cause any kind of issues, since > the next netdev_wait_allrefs_any() will make sure things look correct to > the users again. > > That said, I agree this is good to do to prevent some confusion going to > the users. I wonder if it makes sense to add a comment here noting > that. Otherwise, if I were just freshly reading through the code it > wouldn't follow (all the places where ovs_netdev_link get called are in > the 'create' path). > > WDYT?
I'm not sure if the comment is necessary. We're not creating a device here and it seems clear enough that we shouldn't be linking devices that are not registered, even if there are no races. But I could add something like: /* Do not link devices that are not registered to avoid a potential * race with the NETDEV_UNREGISTER notification in dp_device_event(). */ WDYT? Best regards, Ilya Maximets. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
