Commit a05964f3 authored by Ram Pai's avatar Ram Pai Committed by Linus Torvalds
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[PATCH] shared mounts handling: umount 



An unmount of a mount creates a umount event on the parent.  If the
parent is a shared mount, it gets propagated to all mounts in the peer
group.

Signed-off-by: default avatarRam Pai <linuxram@us.ibm.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 21444403

fs/namespace.c

+38 −18
Original line number Diff line number Diff line
@@ -86,31 +86,44 @@ void free_vfsmnt(struct vfsmount *mnt) 
}



/*

 * Now, lookup_mnt increments the ref count before returning

 * the vfsmount struct.

 * find the first or last mount at @dentry on vfsmount @mnt depending on

 * @dir. If @dir is set return the first mount else return the last mount.

 */

struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)

struct vfsmount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,

			      int dir)

{

	struct list_head *head = mount_hashtable + hash(mnt, dentry);

	struct list_head *tmp = head;

	struct vfsmount *p, *found = NULL;



	spin_lock(&vfsmount_lock);

	for (;;) {

		tmp = tmp->next;

		tmp = dir ? tmp->next : tmp->prev;

		p = NULL;

		if (tmp == head)

			break;

		p = list_entry(tmp, struct vfsmount, mnt_hash);

		if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {

			found = mntget(p);

			found = p;

			break;

		}

	}

	spin_unlock(&vfsmount_lock);

	return found;

}



/*

 * lookup_mnt increments the ref count before returning

 * the vfsmount struct.

 */

struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)

{

	struct vfsmount *child_mnt;

	spin_lock(&vfsmount_lock);

	if ((child_mnt = __lookup_mnt(mnt, dentry, 1)))

		mntget(child_mnt);

	spin_unlock(&vfsmount_lock);

	return child_mnt;

}



static inline int check_mnt(struct vfsmount *mnt)

{

	return mnt->mnt_namespace == current->namespace;
@@ -404,9 +417,12 @@ EXPORT_SYMBOL(may_umount_tree); 
 */

int may_umount(struct vfsmount *mnt)

{

	if (atomic_read(&mnt->mnt_count) > 2)

		return -EBUSY;

	return 0;

	int ret = 0;

	spin_lock(&vfsmount_lock);

	if (propagate_mount_busy(mnt, 2))

		ret = -EBUSY;

	spin_unlock(&vfsmount_lock);

	return ret;

}



EXPORT_SYMBOL(may_umount);
@@ -433,7 +449,7 @@ void release_mounts(struct list_head *head) 
	}

}



void umount_tree(struct vfsmount *mnt, struct list_head *kill)

void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)

{

	struct vfsmount *p;
@@ -442,6 +458,9 @@ void umount_tree(struct vfsmount *mnt, struct list_head *kill) 
		list_add(&p->mnt_hash, kill);

	}



	if (propagate)

		propagate_umount(kill);



	list_for_each_entry(p, kill, mnt_hash) {

		list_del_init(&p->mnt_expire);

		list_del_init(&p->mnt_list);
@@ -450,6 +469,7 @@ void umount_tree(struct vfsmount *mnt, struct list_head *kill) 
		list_del_init(&p->mnt_child);

		if (p->mnt_parent != p)

			mnt->mnt_mountpoint->d_mounted--;

		change_mnt_propagation(p, MS_PRIVATE);

	}

}
@@ -526,9 +546,9 @@ static int do_umount(struct vfsmount *mnt, int flags) 
	event++;



	retval = -EBUSY;

	if (atomic_read(&mnt->mnt_count) == 2 || flags & MNT_DETACH) {

	if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {

		if (!list_empty(&mnt->mnt_list))

			umount_tree(mnt, &umount_list);

			umount_tree(mnt, 1, &umount_list);

		retval = 0;

	}

	spin_unlock(&vfsmount_lock);
@@ -651,7 +671,7 @@ Enomem: 
	if (res) {

		LIST_HEAD(umount_list);

		spin_lock(&vfsmount_lock);

		umount_tree(res, &umount_list);

		umount_tree(res, 0, &umount_list);

		spin_unlock(&vfsmount_lock);

		release_mounts(&umount_list);

	}
@@ -827,7 +847,7 @@ static int do_loopback(struct nameidata *nd, char *old_name, int recurse) 
	if (err) {

		LIST_HEAD(umount_list);

		spin_lock(&vfsmount_lock);

		umount_tree(mnt, &umount_list);

		umount_tree(mnt, 0, &umount_list);

		spin_unlock(&vfsmount_lock);

		release_mounts(&umount_list);

	}
@@ -1023,12 +1043,12 @@ static void expire_mount(struct vfsmount *mnt, struct list_head *mounts, 
	 * Check that it is still dead: the count should now be 2 - as

	 * contributed by the vfsmount parent and the mntget above

	 */

	if (atomic_read(&mnt->mnt_count) == 2) {

	if (!propagate_mount_busy(mnt, 2)) {

		/* delete from the namespace */

		touch_namespace(mnt->mnt_namespace);

		list_del_init(&mnt->mnt_list);

		mnt->mnt_namespace = NULL;

		umount_tree(mnt, umounts);

		umount_tree(mnt, 1, umounts);

		spin_unlock(&vfsmount_lock);

	} else {

		/*
@@ -1647,7 +1667,7 @@ void __put_namespace(struct namespace *namespace) 
	spin_unlock(&vfsmount_lock);

	down_write(&namespace_sem);

	spin_lock(&vfsmount_lock);

	umount_tree(root, &umount_list);

	umount_tree(root, 0, &umount_list);

	spin_unlock(&vfsmount_lock);

	up_write(&namespace_sem);

	release_mounts(&umount_list);

fs/pnode.c

+86 −1
Original line number Diff line number Diff line
@@ -99,9 +99,94 @@ out: 
	while (!list_empty(&tmp_list)) {

		child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);

		list_del_init(&child->mnt_hash);

		umount_tree(child, &umount_list);

		umount_tree(child, 0, &umount_list);

	}

	spin_unlock(&vfsmount_lock);

	release_mounts(&umount_list);

	return ret;

}



/*

 * return true if the refcount is greater than count

 */

static inline int do_refcount_check(struct vfsmount *mnt, int count)

{

	int mycount = atomic_read(&mnt->mnt_count);

	return (mycount > count);

}



/*

 * check if the mount 'mnt' can be unmounted successfully.

 * @mnt: the mount to be checked for unmount

 * NOTE: unmounting 'mnt' would naturally propagate to all

 * other mounts its parent propagates to.

 * Check if any of these mounts that **do not have submounts**

 * have more references than 'refcnt'. If so return busy.

 */

int propagate_mount_busy(struct vfsmount *mnt, int refcnt)

{

	struct vfsmount *m, *child;

	struct vfsmount *parent = mnt->mnt_parent;

	int ret = 0;



	if (mnt == parent)

		return do_refcount_check(mnt, refcnt);



	/*

	 * quickly check if the current mount can be unmounted.

	 * If not, we don't have to go checking for all other

	 * mounts

	 */

	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))

		return 1;



	for (m = propagation_next(parent, parent); m;

	     		m = propagation_next(m, parent)) {

		child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);

		if (child && list_empty(&child->mnt_mounts) &&

		    (ret = do_refcount_check(child, 1)))

			break;

	}

	return ret;

}



/*

 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its

 * parent propagates to.

 */

static void __propagate_umount(struct vfsmount *mnt)

{

	struct vfsmount *parent = mnt->mnt_parent;

	struct vfsmount *m;



	BUG_ON(parent == mnt);



	for (m = propagation_next(parent, parent); m;

			m = propagation_next(m, parent)) {



		struct vfsmount *child = __lookup_mnt(m,

					mnt->mnt_mountpoint, 0);

		/*

		 * umount the child only if the child has no

		 * other children

		 */

		if (child && list_empty(&child->mnt_mounts)) {

			list_del(&child->mnt_hash);

			list_add_tail(&child->mnt_hash, &mnt->mnt_hash);

		}

	}

}



/*

 * collect all mounts that receive propagation from the mount in @list,

 * and return these additional mounts in the same list.

 * @list: the list of mounts to be unmounted.

 */

int propagate_umount(struct list_head *list)

{

	struct vfsmount *mnt;



	list_for_each_entry(mnt, list, mnt_hash)

		__propagate_umount(mnt);

	return 0;

}

fs/pnode.h

+2 −0
Original line number Diff line number Diff line
@@ -29,4 +29,6 @@ static inline void set_mnt_shared(struct vfsmount *mnt) 
void change_mnt_propagation(struct vfsmount *, int);

int propagate_mnt(struct vfsmount *, struct dentry *, struct vfsmount *,

		struct list_head *);

int propagate_umount(struct list_head *);

int propagate_mount_busy(struct vfsmount *, int);

#endif /* _LINUX_PNODE_H */

include/linux/dcache.h

+1 −0
Original line number Diff line number Diff line
@@ -329,6 +329,7 @@ static inline int d_mountpoint(struct dentry *dentry) 
}



extern struct vfsmount *lookup_mnt(struct vfsmount *, struct dentry *);

extern struct vfsmount *__lookup_mnt(struct vfsmount *, struct dentry *, int);

extern struct dentry *lookup_create(struct nameidata *nd, int is_dir);



extern int sysctl_vfs_cache_pressure;

include/linux/fs.h

+1 −1
Original line number Diff line number Diff line
@@ -1251,7 +1251,7 @@ extern int unregister_filesystem(struct file_system_type *); 
extern struct vfsmount *kern_mount(struct file_system_type *);

extern int may_umount_tree(struct vfsmount *);

extern int may_umount(struct vfsmount *);

extern void umount_tree(struct vfsmount *, struct list_head *);

extern void umount_tree(struct vfsmount *, int, struct list_head *);

extern void release_mounts(struct list_head *);

extern long do_mount(char *, char *, char *, unsigned long, void *);

extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);

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