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Commit 80b5dce8 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Al Viro
Browse files

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: default avatarEric W. Biederman <ebiederman@twitter.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent e2dfa935

fs/mount.h

+9 −0
Original line number Diff line number Diff line
@@ -87,6 +87,15 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *); 


extern bool legitimize_mnt(struct vfsmount *, unsigned);



extern void __detach_mounts(struct dentry *dentry);



static inline void detach_mounts(struct dentry *dentry)

{

	if (!d_mountpoint(dentry))

		return;

	__detach_mounts(dentry);

}



static inline void get_mnt_ns(struct mnt_namespace *ns)

{

	atomic_inc(&ns->count);

fs/namespace.c

+31 −0
Original line number Diff line number Diff line
@@ -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?

 */