"Lino Sanfilippo" <LinoSanfilippo@xxxxxx> writes: > Hi, > >> >> MTU change and set channels operations are implemented as netvsc device >> re-creation destroying internal structures (struct net_device stays). This >> is really unfortunate but there is no support from Hyper-V host to do it >> in a different way. Such re-creation is unsurprisingly racy, Haiyang >> reported a crash when netvsc_change_mtu() is racing with >> netvsc_link_change() but I was able to identify additional races upon >> investigation. Both netvsc_set_channels() and netvsc_change_mtu() race >> against: >> 1) netvsc_link_change() >> 2) netvsc_remove() >> 3) netvsc_send() >> > > after having a look into this driver I got the impression that you are working around an > unfortunate implementation of the shutdown sequence in the remove function: > If you do unregister_netdev() first instead of resource cleanup then neither set_channels() > nor change_mtu() can race with remove(). This is since after unregister_netdev() returns > the netdev is not longer available from userspace and thus neither set_channels nor > change_mtu can be called anymore (note that all of these functions are protected by the > rtnl_lock). It's worse: before the patch series we get 'struct hv_device' (as it is called from core VMBus code and we simply cannot get to 'struct net_device' we need without traveling through 'struct netvsc_device'. This structure is removed and re-created by both netvsc_set_channels() and netvsc_change_mtu(). > > To avoid the race between netvsc_change_mtu()/netvsc_set_channels() and netvsc_link_change() > you have to stop the concerning worker thread (dwork) before you call netvsc_close() and > restart it once the device is up again. Yes, but we also need to guarantee this won't get rescheduled so we need a flag for that. The appropriate flag is start_remove but only after we move it from a structure we remove. -- Vitaly _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
