Jens Markwardt reported a regression in the linux-next runs. with "umh: fix processed error when UMH_WAIT_PROC is used" (from linux-next) a linux bridge with an KVM guests no longer activates : without patch # ip addr show dev virbr1 6: virbr1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 52:54:00:1e:3f:c0 brd ff:ff:ff:ff:ff:ff inet 192.168.254.254/24 brd 192.168.254.255 scope global virbr1 valid_lft forever preferred_lft forever with this patch the bridge stays DOWN with NO-CARRIER # ip addr show dev virbr1 6: virbr1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000 link/ether 52:54:00:1e:3f:c0 brd ff:ff:ff:ff:ff:ff inet 192.168.254.254/24 brd 192.168.254.255 scope global virbr1 valid_lft forever preferred_lft forever This was bisected in linux-next. Reverting from linux-next also fixes the issue. Any idea? Christian