tree ad0a4f5f256f55ed8115c30823c0c967cbedba13
parent 84d17192d2afd52aeba88c71ae4959a015f56a38
author Al Viro <viro@zeniv.linux.org.uk> 1363458916 -0400
committer Al Viro <viro@zeniv.linux.org.uk> 1365531172 -0400

saner umount_tree()/release_mounts(), part 1

global list of release_mounts() fodder, protected by namespace_sem;
eventually, all umount_tree() callers will use it as kill list.
Helper picking the contents of that list, releasing namespace_sem
and doing release_mounts() on what it got.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>