mnt: support ns lookup

Move the mount namespace to the generic ns lookup infrastructure.
This allows us to drop a bunch of members from struct mnt_namespace.

Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/mount.h

@@ -17,11 +17,7 @@ struct mnt_namespace {
 	};
 	struct user_namespace	*user_ns;
 	struct ucounts		*ucounts;
-	u64			seq;	/* Sequence number to prevent loops */
-	union {
-		wait_queue_head_t	poll;
-		struct rcu_head		mnt_ns_rcu;
-	};
+	wait_queue_head_t	poll;
 	u64			seq_origin; /* Sequence number of origin mount namespace */
 	u64 event;
 #ifdef CONFIG_FSNOTIFY
@@ -30,8 +26,6 @@ struct mnt_namespace {
 #endif
 	unsigned int		nr_mounts; /* # of mounts in the namespace */
 	unsigned int		pending_mounts;
-	struct rb_node		mnt_ns_tree_node; /* node in the mnt_ns_tree */
-	struct list_head	mnt_ns_list; /* entry in the sequential list of mounts namespace */
 	refcount_t		passive; /* number references not pinning @mounts */
 } __randomize_layout;
 
@@ -173,7 +167,7 @@ static inline bool is_local_mountpoint(const struct dentry *dentry)
 
 static inline bool is_anon_ns(struct mnt_namespace *ns)
 {
-	return ns->seq == 0;
+	return ns->ns.ns_id == 0;
 }
 
 static inline bool anon_ns_root(const struct mount *m)

fs/namespace.c

@@ -33,6 +33,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/mnt_idmapping.h>
 #include <linux/pidfs.h>
+#include <linux/nstree.h>
 
 #include "pnode.h"
 #include "internal.h"
@@ -80,13 +81,10 @@ static DECLARE_RWSEM(namespace_sem);
 static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
 static struct mnt_namespace *emptied_ns; /* protected by namespace_sem */
-static DEFINE_SEQLOCK(mnt_ns_tree_lock);
 
 #ifdef CONFIG_FSNOTIFY
 LIST_HEAD(notify_list); /* protected by namespace_sem */
 #endif
-static struct rb_root mnt_ns_tree = RB_ROOT; /* protected by mnt_ns_tree_lock */
-static LIST_HEAD(mnt_ns_list); /* protected by mnt_ns_tree_lock */
 
 enum mount_kattr_flags_t {
 	MOUNT_KATTR_RECURSE		= (1 << 0),
@@ -119,53 +117,12 @@ __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
 
 static inline struct mnt_namespace *node_to_mnt_ns(const struct rb_node *node)
 {
+	struct ns_common *ns;
+
 	if (!node)
 		return NULL;
-	return rb_entry(node, struct mnt_namespace, mnt_ns_tree_node);
-}
-
-static int mnt_ns_cmp(struct rb_node *a, const struct rb_node *b)
-{
-	struct mnt_namespace *ns_a = node_to_mnt_ns(a);
-	struct mnt_namespace *ns_b = node_to_mnt_ns(b);
-	u64 seq_a = ns_a->seq;
-	u64 seq_b = ns_b->seq;
-
-	if (seq_a < seq_b)
-		return -1;
-	if (seq_a > seq_b)
-		return 1;
-	return 0;
-}
-
-static inline void mnt_ns_tree_write_lock(void)
-{
-	write_seqlock(&mnt_ns_tree_lock);
-}
-
-static inline void mnt_ns_tree_write_unlock(void)
-{
-	write_sequnlock(&mnt_ns_tree_lock);
-}
-
-static void mnt_ns_tree_add(struct mnt_namespace *ns)
-{
-	struct rb_node *node, *prev;
-
-	mnt_ns_tree_write_lock();
-	node = rb_find_add_rcu(&ns->mnt_ns_tree_node, &mnt_ns_tree, mnt_ns_cmp);
-	/*
-	 * If there's no previous entry simply add it after the
-	 * head and if there is add it after the previous entry.
-	 */
-	prev = rb_prev(&ns->mnt_ns_tree_node);
-	if (!prev)
-		list_add_rcu(&ns->mnt_ns_list, &mnt_ns_list);
-	else
-		list_add_rcu(&ns->mnt_ns_list, &node_to_mnt_ns(prev)->mnt_ns_list);
-	mnt_ns_tree_write_unlock();
-
-	WARN_ON_ONCE(node);
+	ns = rb_entry(node, struct ns_common, ns_tree_node);
+	return container_of(ns, struct mnt_namespace, ns);
 }
 
 static void mnt_ns_release(struct mnt_namespace *ns)
@@ -181,32 +138,16 @@ DEFINE_FREE(mnt_ns_release, struct mnt_namespace *, if (_T) mnt_ns_release(_T))
 
 static void mnt_ns_release_rcu(struct rcu_head *rcu)
 {
-	mnt_ns_release(container_of(rcu, struct mnt_namespace, mnt_ns_rcu));
+	mnt_ns_release(container_of(rcu, struct mnt_namespace, ns.ns_rcu));
 }
 
 static void mnt_ns_tree_remove(struct mnt_namespace *ns)
 {
 	/* remove from global mount namespace list */
-	if (!RB_EMPTY_NODE(&ns->mnt_ns_tree_node)) {
-		mnt_ns_tree_write_lock();
-		rb_erase(&ns->mnt_ns_tree_node, &mnt_ns_tree);
-		list_bidir_del_rcu(&ns->mnt_ns_list);
-		mnt_ns_tree_write_unlock();
-	}
+	if (ns_tree_active(ns))
+		ns_tree_remove(ns);
 
-	call_rcu(&ns->mnt_ns_rcu, mnt_ns_release_rcu);
-}
-
-static int mnt_ns_find(const void *key, const struct rb_node *node)
-{
-	const u64 mnt_ns_id = *(u64 *)key;
-	const struct mnt_namespace *ns = node_to_mnt_ns(node);
-
-	if (mnt_ns_id < ns->seq)
-		return -1;
-	if (mnt_ns_id > ns->seq)
-		return 1;
-	return 0;
+	call_rcu(&ns->ns.ns_rcu, mnt_ns_release_rcu);
 }
 
 /*
@@ -225,28 +166,21 @@ static int mnt_ns_find(const void *key, const struct rb_node *node)
  */
 static struct mnt_namespace *lookup_mnt_ns(u64 mnt_ns_id)
 {
-	struct mnt_namespace *ns;
-	struct rb_node *node;
-	unsigned int seq;
+	struct mnt_namespace *mnt_ns;
+	struct ns_common *ns;
 
 	guard(rcu)();
-	do {
-		seq = read_seqbegin(&mnt_ns_tree_lock);
-		node = rb_find_rcu(&mnt_ns_id, &mnt_ns_tree, mnt_ns_find);
-		if (node)
-			break;
-	} while (read_seqretry(&mnt_ns_tree_lock, seq));
-
-	if (!node)
+	ns = ns_tree_lookup_rcu(mnt_ns_id, CLONE_NEWNS);
+	if (!ns)
 		return NULL;
 
 	/*
 	 * The last reference count is put with RCU delay so we can
 	 * unconditonally acquire a reference here.
 	 */
-	ns = node_to_mnt_ns(node);
-	refcount_inc(&ns->passive);
-	return ns;
+	mnt_ns = container_of(ns, struct mnt_namespace, ns);
+	refcount_inc(&mnt_ns->passive);
+	return mnt_ns;
 }
 
 static inline void lock_mount_hash(void)
@@ -1017,7 +951,7 @@ static inline bool check_anonymous_mnt(struct mount *mnt)
 		return false;
 
 	seq = mnt->mnt_ns->seq_origin;
-	return !seq || (seq == current->nsproxy->mnt_ns->seq);
+	return !seq || (seq == current->nsproxy->mnt_ns->ns.ns_id);
 }
 
 /*
@@ -2152,19 +2086,16 @@ struct ns_common *from_mnt_ns(struct mnt_namespace *mnt)
 
 struct mnt_namespace *get_sequential_mnt_ns(struct mnt_namespace *mntns, bool previous)
 {
+	struct ns_common *ns;
+
 	guard(rcu)();
 
 	for (;;) {
-		struct list_head *list;
+		ns = ns_tree_adjoined_rcu(mntns, previous);
+		if (IS_ERR(ns))
+			return ERR_CAST(ns);
 
-		if (previous)
-			list = rcu_dereference(list_bidir_prev_rcu(&mntns->mnt_ns_list));
-		else
-			list = rcu_dereference(list_next_rcu(&mntns->mnt_ns_list));
-		if (list_is_head(list, &mnt_ns_list))
-			return ERR_PTR(-ENOENT);
-
-		mntns = list_entry_rcu(list, struct mnt_namespace, mnt_ns_list);
+		mntns = to_mnt_ns(ns);
 
 		/*
 		 * The last passive reference count is put with RCU
@@ -2204,7 +2135,7 @@ static bool mnt_ns_loop(struct dentry *dentry)
 	if (!mnt_ns)
 		return false;
 
-	return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
+	return current->nsproxy->mnt_ns->ns.ns_id >= mnt_ns->ns.ns_id;
 }
 
 struct mount *copy_tree(struct mount *src_root, struct dentry *dentry,
@@ -3080,7 +3011,7 @@ static struct file *open_detached_copy(struct path *path, bool recursive)
 		if (is_anon_ns(src_mnt_ns))
 			ns->seq_origin = src_mnt_ns->seq_origin;
 		else
-			ns->seq_origin = src_mnt_ns->seq;
+			ns->seq_origin = src_mnt_ns->ns.ns_id;
 	}
 
 	mnt = __do_loopback(path, recursive);
@@ -4156,15 +4087,6 @@ static void free_mnt_ns(struct mnt_namespace *ns)
 	mnt_ns_tree_remove(ns);
 }
 
-/*
- * Assign a sequence number so we can detect when we attempt to bind
- * mount a reference to an older mount namespace into the current
- * mount namespace, preventing reference counting loops.  A 64bit
- * number incrementing at 10Ghz will take 12,427 years to wrap which
- * is effectively never, so we can ignore the possibility.
- */
-static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
-
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)
 {
 	struct mnt_namespace *new_ns;
@@ -4188,11 +4110,9 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool a
 		return ERR_PTR(ret);
 	}
 	if (!anon)
-		new_ns->seq = atomic64_inc_return(&mnt_ns_seq);
+		ns_tree_gen_id(&new_ns->ns);
 	refcount_set(&new_ns->passive, 1);
 	new_ns->mounts = RB_ROOT;
-	INIT_LIST_HEAD(&new_ns->mnt_ns_list);
-	RB_CLEAR_NODE(&new_ns->mnt_ns_tree_node);
 	init_waitqueue_head(&new_ns->poll);
 	new_ns->user_ns = get_user_ns(user_ns);
 	new_ns->ucounts = ucounts;
@@ -4278,7 +4198,7 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 	if (pwdmnt)
 		mntput(pwdmnt);
 
-	mnt_ns_tree_add(new_ns);
+	ns_tree_add_raw(new_ns);
 	return new_ns;
 }
 
@@ -5397,7 +5317,7 @@ static int statmount_sb_source(struct kstatmount *s, struct seq_file *seq)
 static void statmount_mnt_ns_id(struct kstatmount *s, struct mnt_namespace *ns)
 {
 	s->sm.mask |= STATMOUNT_MNT_NS_ID;
-	s->sm.mnt_ns_id = ns->seq;
+	s->sm.mnt_ns_id = ns->ns.ns_id;
 }
 
 static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
@@ -6102,7 +6022,6 @@ static void __init init_mount_tree(void)
 	ns = alloc_mnt_ns(&init_user_ns, true);
 	if (IS_ERR(ns))
 		panic("Can't allocate initial namespace");
-	ns->seq = atomic64_inc_return(&mnt_ns_seq);
 	ns->ns.inum = PROC_MNT_INIT_INO;
 	m = real_mount(mnt);
 	ns->root = m;
@@ -6117,7 +6036,7 @@ static void __init init_mount_tree(void)
 	set_fs_pwd(current->fs, &root);
 	set_fs_root(current->fs, &root);
 
-	mnt_ns_tree_add(ns);
+	ns_tree_add(ns);
 }
 
 void __init mnt_init(void)

fs/nsfs.c

@@ -139,7 +139,7 @@ static int copy_ns_info_to_user(const struct mnt_namespace *mnt_ns,
 	 * the size value will be set to the size the kernel knows about.
 	 */
 	kinfo->size		= min(usize, sizeof(*kinfo));
-	kinfo->mnt_ns_id	= mnt_ns->seq;
+	kinfo->mnt_ns_id	= mnt_ns->ns.ns_id;
 	kinfo->nr_mounts	= READ_ONCE(mnt_ns->nr_mounts);
 	/* Subtract the root mount of the mount namespace. */
 	if (kinfo->nr_mounts)
@@ -221,7 +221,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
 
 		mnt_ns = container_of(ns, struct mnt_namespace, ns);
 		idp = (__u64 __user *)arg;
-		id = mnt_ns->seq;
+		id = mnt_ns->ns.ns_id;
 		return put_user(id, idp);
 	}
 	case NS_GET_PID_FROM_PIDNS: