tree 90b7a4f30c050d37f7ec436b63c8f9d7816199f0
parent e2dfa935464272395b4f35f4cc74ffcc87418b84
author Eric W. Biederman <ebiederman@twitter.com> 1380789078 -0700
committer Al Viro <viro@zeniv.linux.org.uk> 1412836735 -0400

vfs: Add a function to lazily unmount all mounts from any dentry.

The new function detach_mounts comes in two pieces.  The first piece
is a static inline test of d_mounpoint that returns immediately
without taking any locks if d_mounpoint is not set.  In the common
case when mountpoints are absent this allows the vfs to continue
running with it's same cacheline foot print.

The second piece of detach_mounts __detach_mounts actually does the
work and it assumes that a mountpoint is present so it is slow and
takes namespace_sem for write, and then locks the mount hash (aka
mount_lock) after a struct mountpoint has been found.

With those two locks held each entry on the list of mounts on a
mountpoint is selected and lazily unmounted until all of the mount
have been lazily unmounted.

v7: Wrote a proper change description and removed the changelog
    documenting deleted wrong turns.

Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>