From 80b5dce8c59b0de1ed6e403b8298e02dcb4db64b Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Thu, 3 Oct 2013 01:31:18 -0700 Subject: 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 Signed-off-by: Al Viro --- fs/namespace.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'fs/namespace.c') diff --git a/fs/namespace.c b/fs/namespace.c index 88fc3f4d77ed..00e5b1efa591 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1468,6 +1468,37 @@ static int do_umount(struct mount *mnt, int flags) return retval; } +/* + * __detach_mounts - lazily unmount all mounts on the specified dentry + * + * During unlink, rmdir, and d_drop it is possible to loose the path + * to an existing mountpoint, and wind up leaking the mount. + * detach_mounts allows lazily unmounting those mounts instead of + * leaking them. + * + * The caller may hold dentry->d_inode->i_mutex. + */ +void __detach_mounts(struct dentry *dentry) +{ + struct mountpoint *mp; + struct mount *mnt; + + namespace_lock(); + mp = lookup_mountpoint(dentry); + if (!mp) + goto out_unlock; + + lock_mount_hash(); + while (!hlist_empty(&mp->m_list)) { + mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list); + umount_tree(mnt, 2); + } + unlock_mount_hash(); + put_mountpoint(mp); +out_unlock: + namespace_unlock(); +} + /* * Is the caller allowed to modify his namespace? */ -- cgit v1.2.3-59-g8ed1b