Simplify the rules for mount refcounts. Current rules include: * being a namespace root => +1 * being someone's child => +1 * being someone's child => +1 to parent's refcount, unless you've already been through umount_tree(). The last part is not needed at all. It makes for more places where need to decrement refcounts and it creates an asymmetry between the situations for something that has never been a part of a namespace and something that left one, both for no good reason. If mount's refcount has additions from its children, we know that * it's either someone's child itself (and will remain so until umount_tree(), at which point contributions from children will disappear), or * or is the root of namespace (and will remain such until it either becomes someone's child in another namespace or goes through umount_tree()), or * it is the root of some tree copy, and is currently pinned by the caller of copy_tree() (and remains such until it either gets into namespace, or goes to umount_tree()). In all cases we already have contribution(s) to refcount that will last as long as the contribution from children remains. In other words, the lifetime is not affected by refcount contributions from children. It might be useful for "is it busy" checks, but those are actually no harder to express without it. NB: propagate_mnt_busy() part is an equivalent transformation, ugly as it is; the current logics is actually wrong and may give false negatives, but fixing that is for a separate patch (probably earlier in the queue). Reviewed-by: Christian Brauner <brauner@kernel.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>