3 files changed, 95 insertions, 4 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 8ca6317cb401..cefa1d9939b0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -41,6 +41,7 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
 
 static int event;
 static DEFINE_IDA(mnt_id_ida);
+static DEFINE_IDA(mnt_group_ida);
 
 static struct list_head *mount_hashtable __read_mostly;
 static struct kmem_cache *mnt_cache __read_mostly;
@@ -83,6 +84,28 @@ static void mnt_free_id(struct vfsmount *mnt)
         spin_unlock(&vfsmount_lock);
 }
 
+/*
+ * Allocate a new peer group ID
+ *
+ * mnt_group_ida is protected by namespace_sem
+ */
+static int mnt_alloc_group_id(struct vfsmount *mnt)
+{
+        if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
+                return -ENOMEM;
+
+        return ida_get_new_above(&mnt_group_ida, 1, &mnt->mnt_group_id);
+}
+
+/*
+ * Release a peer group ID
+ */
+void mnt_release_group_id(struct vfsmount *mnt)
+{
+        ida_remove(&mnt_group_ida, mnt->mnt_group_id);
+        mnt->mnt_group_id = 0;
+}
+
 struct vfsmount *alloc_vfsmnt(const char *name)
 {
         struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
@@ -533,6 +556,17 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
         struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
 
         if (mnt) {
+                if (flag & (CL_SLAVE | CL_PRIVATE))
+                        mnt->mnt_group_id = 0; /* not a peer of original */
+                else
+                        mnt->mnt_group_id = old->mnt_group_id;
+
+                if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
+                        int err = mnt_alloc_group_id(mnt);
+                        if (err)
+                                goto out_free;
+                }
+
                 mnt->mnt_flags = old->mnt_flags;
                 atomic_inc(&sb->s_active);
                 mnt->mnt_sb = sb;
@@ -562,6 +596,10 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
                 }
         }
         return mnt;
+
+ out_free:
+        free_vfsmnt(mnt);
+        return NULL;
 }
 
 static inline void __mntput(struct vfsmount *mnt)
@@ -1142,6 +1180,33 @@ void drop_collected_mounts(struct vfsmount *mnt)
         release_mounts(&umount_list);
 }
 
+static void cleanup_group_ids(struct vfsmount *mnt, struct vfsmount *end)
+{
+        struct vfsmount *p;
+
+        for (p = mnt; p != end; p = next_mnt(p, mnt)) {
+                if (p->mnt_group_id && !IS_MNT_SHARED(p))
+                        mnt_release_group_id(p);
+        }
+}
+
+static int invent_group_ids(struct vfsmount *mnt, bool recurse)
+{
+        struct vfsmount *p;
+
+        for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
+                if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
+                        int err = mnt_alloc_group_id(p);
+                        if (err) {
+                                cleanup_group_ids(mnt, p);
+                                return err;
+                        }
+                }
+        }
+
+        return 0;
+}
+
 /*
  *  @source_mnt : mount tree to be attached
  *  @nd         : place the mount tree @source_mnt is attached
@@ -1212,9 +1277,16 @@ static int attach_recursive_mnt(struct vfsmount *source_mnt,
         struct vfsmount *dest_mnt = path->mnt;
         struct dentry *dest_dentry = path->dentry;
         struct vfsmount *child, *p;
+        int err;
 
-        if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
-                return -EINVAL;
+        if (IS_MNT_SHARED(dest_mnt)) {
+                err = invent_group_ids(source_mnt, true);
+                if (err)
+                        goto out;
+        }
+        err = propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list);
+        if (err)
+                goto out_cleanup_ids;
 
         if (IS_MNT_SHARED(dest_mnt)) {
                 for (p = source_mnt; p; p = next_mnt(p, source_mnt))
@@ -1237,6 +1309,12 @@ static int attach_recursive_mnt(struct vfsmount *source_mnt,
         }
         spin_unlock(&vfsmount_lock);
         return 0;
+
+ out_cleanup_ids:
+        if (IS_MNT_SHARED(dest_mnt))
+                cleanup_group_ids(source_mnt, NULL);
+ out:
+        return err;
 }
 
 static int graft_tree(struct vfsmount *mnt, struct path *path)
@@ -1277,6 +1355,7 @@ static noinline int do_change_type(struct nameidata *nd, int flag)
         struct vfsmount *m, *mnt = nd->path.mnt;
         int recurse = flag & MS_REC;
         int type = flag & ~MS_REC;
+        int err = 0;
 
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
@@ -1285,12 +1364,20 @@ static noinline int do_change_type(struct nameidata *nd, int flag)
                 return -EINVAL;
 
         down_write(&namespace_sem);
+        if (type == MS_SHARED) {
+                err = invent_group_ids(mnt, recurse);
+                if (err)
+                        goto out_unlock;
+        }
+
         spin_lock(&vfsmount_lock);
         for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
                 change_mnt_propagation(m, type);
         spin_unlock(&vfsmount_lock);
+
+ out_unlock:
         up_write(&namespace_sem);
-        return 0;
+        return err;
 }
 
 /*
diff --git a/fs/pnode.c b/fs/pnode.c
index f968e35d9785..d18d66491a01 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -46,7 +46,11 @@ static int do_make_slave(struct vfsmount *mnt)
                 if (peer_mnt == mnt)
                         peer_mnt = NULL;
         }
+        if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
+                mnt_release_group_id(mnt);
+
         list_del_init(&mnt->mnt_share);
+        mnt->mnt_group_id = 0;
 
         if (peer_mnt)
                 master = peer_mnt;
@@ -68,7 +72,6 @@ static int do_make_slave(struct vfsmount *mnt)
         }
         mnt->mnt_master = master;
         CLEAR_MNT_SHARED(mnt);
-        INIT_LIST_HEAD(&mnt->mnt_slave_list);
         return 0;
 }
 
diff --git a/include/linux/mount.h b/include/linux/mount.h
index f0dfb17ffccc..b4836d58f428 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -57,6 +57,7 @@ struct vfsmount {
         struct vfsmount *mnt_master;    /* slave is on master->mnt_slave_list */
         struct mnt_namespace *mnt_ns;   /* containing namespace */
         int mnt_id;                     /* mount identifier */
+        int mnt_group_id;               /* peer group identifier */
         /*
          * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount
          * to let these frequently modified fields in a separate cache line