[Bridge] linux-next: umh: fix processed error when UMH_WAIT_PROC is used seems to break linux bridge on s390x (bisected)

[Christian Borntraeger]

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