On Thu, Aug 02, 2018 at 02:04:12PM -0700, Nambiar, Amritha wrote: > On 8/1/2018 5:11 PM, Andrei Vagin wrote: > > On Tue, Jul 10, 2018 at 07:28:49PM -0700, Nambiar, Amritha wrote: > >> With this patch series, I introduced static_key for XPS maps > >> (xps_needed), so static_key_slow_inc() is used to switch branches. The > >> definition of static_key_slow_inc() has cpus_read_lock in place. In the > >> virtio_net driver, XPS queues are initialized after setting the > >> queue:cpu affinity in virtnet_set_affinity() which is already protected > >> within cpus_read_lock. Hence, the warning here trying to acquire > >> cpus_read_lock when it is already held. > >> > >> A quick fix for this would be to just extract netif_set_xps_queue() out > >> of the lock by simply wrapping it with another put/get_online_cpus > >> (unlock right before and hold lock right after). > > > > virtnet_set_affinity() is called from virtnet_cpu_online(), which is > > called under cpus_read_lock too. > > > > It looks like now we can't call netif_set_xps_queue() from cpu hotplug > > callbacks. > > > > I can suggest a very straightforward fix for this problem. The patch is > > attached. > > > > Thanks for looking into this. I was thinking of fixing this in the > virtio_net driver by moving the XPS initialization (and have a new > get_affinity utility) in the ndo_open (so it is together with other tx > preparation) instead of probe. Your patch solves this in general for > setting up cpu hotplug callbacks which is under cpus_read_lock. I like this too. Could you repost in a standard way (inline, with your signoff etc) so we can ack this for net-next? > >> But this may not a > >> clean solution. It'd help if I can get suggestions on what would be a > >> clean option to fix this without extensively changing the code in > >> virtio_net. Is it mandatory to protect the affinitization with > >> read_lock? I don't see similar lock in other drivers while setting the > >> affinity. I understand this warning should go away, but isn't it safe to > >> have multiple readers. > >> > >>> On Fri, Jun 29, 2018 at 09:27:07PM -0700, Amritha Nambiar wrote: _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
