[PATCH review 11/11] mnt: Honor MNT_LOCKED when detaching mounts

Al Viro viro at ZenIV.linux.org.uk
Wed Jan 7 18:43:34 UTC 2015

On Mon, Jan 05, 2015 at 02:46:27PM -0600, Eric W. Biederman wrote:
> Modify umount(MNT_DETACH) to keep mounts in the hash table that are
> locked to their parent mounts, when the parent is lazily unmounted.
> In doing this invert the reference count so that the parent holds a
> reference to the children instead of the children holding a reference
> to the parent.
> Then in mntput_no_expire detach the children and in cleanup_mnt mntput
> the children and dput the dentry they were mounted on.
> In __detach_mounts if there are any mounts that have been unmounted
> but still are on the list of mounts of a mountpoint, detach those
> mounts and schedule them to be mntput and their reference to the dentry
> to be put when it becomes safe to sleep.

Explicit description of your new refcounting rules, please.  What's more,
how do those non-pinning children interact with e.g. copy_tree()?

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