From: Ram Pai <[email protected]>
Date: 1131402017 -0500
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: Ram Pai ([email protected])
Signed-off-by: Al Viro <[email protected]>
---
fs/namespace.c | 56 +++++++++++++++++++++----------
fs/pnode.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++-
fs/pnode.h | 2 +
include/linux/dcache.h | 1 +
include/linux/fs.h | 2 +
5 files changed, 128 insertions(+), 20 deletions(-)
9eeda77dfca5c1193fcf9702d2921e3545362c19
diff --git a/fs/namespace.c b/fs/namespace.c
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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 *he
}
}
-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, s
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, s
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 *mn
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
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
* 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 *n
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);
diff --git a/fs/pnode.c b/fs/pnode.c
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -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;
+}
diff --git a/fs/pnode.h b/fs/pnode.h
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -29,4 +29,6 @@ static inline void set_mnt_shared(struct
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 */
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -329,6 +329,7 @@ static inline int d_mountpoint(struct de
}
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;
diff --git a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1251,7 +1251,7 @@ extern int unregister_filesystem(struct
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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