In the multi-master case, on master switch the new master takes the
previously active master lock in write mode, and then evicts all
buffers. Any clients to previous masters will then block on that lock
when trying to validate a buffer. fbdev also acts as a virtual master
wrt this.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com> Signed-off-by: Jakob Bornecrantz <jakob@vmware.com> Signed-off-by: Dave Airlie <airlied@redhat.com>