Merge tag 'vfs-6.14-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs mount updates from Christian Brauner:

 - Add a mountinfo program to demonstrate statmount()/listmount()

   Add a new "mountinfo" sample userland program that demonstrates how
   to use statmount() and listmount() to get at the same info that
   /proc/pid/mountinfo provides

 - Remove pointless nospec.h include

 - Prepend statmount.mnt_opts string with security_sb_mnt_opts()

   Currently these mount options aren't accessible via statmount()

 - Add new mount namespaces to mount namespace rbtree outside of the
   namespace semaphore

 - Lockless mount namespace lookup

   Currently we take the read lock when looking for a mount namespace to
   list mounts in. We can make this lockless. The simple search case can
   just use a sequence counter to detect concurrent changes to the
   rbtree

   For walking the list of mount namespaces sequentially via nsfs we
   keep a separate rcu list as rb_prev() and rb_next() aren't usable
   safely with rcu. Currently there is no primitive for retrieving the
   previous list member. To do this we need a new deletion primitive
   that doesn't poison the prev pointer and a corresponding retrieval
   helper

   Since creating mount namespaces is a relatively rare event compared
   with querying mounts in a foreign mount namespace this is worth it.
   Once libmount and systemd pick up this mechanism to list mounts in
   foreign mount namespaces this will be used very frequently

     - Add extended selftests for lockless mount namespace iteration

     - Add a sample program to list all mounts on the system, i.e., in
       all mount namespaces

 - Improve mount namespace iteration performance

   Make finding the last or first mount to start iterating the mount
   namespace from an O(1) operation and add selftests for iterating the
   mount table starting from the first and last mount

 - Use an xarray for the old mount id

   While the ida does use the xarray internally we can use it explicitly
   which allows us to increment the unique mount id under the xa lock.
   This allows us to remove the atomic as we're now allocating both ids
   in one go

 - Use a shared header for vfs sample programs

 - Fix build warnings for new sample program to list all mounts

* tag 'vfs-6.14-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  samples/vfs: fix build warnings
  samples/vfs: use shared header
  samples/vfs/mountinfo: Use __u64 instead of uint64_t
  fs: remove useless lockdep assertion
  fs: use xarray for old mount id
  selftests: add listmount() iteration tests
  fs: cache first and last mount
  samples: add test-list-all-mounts
  selftests: remove unneeded include
  selftests: add tests for mntns iteration
  seltests: move nsfs into filesystems subfolder
  fs: simplify rwlock to spinlock
  fs: lockless mntns lookup for nsfs
  rculist: add list_bidir_{del,prev}_rcu()
  fs: lockless mntns rbtree lookup
  fs: add mount namespace to rbtree late
  fs: prepend statmount.mnt_opts string with security_sb_mnt_opts()
  mount: remove inlude/nospec.h include
  samples: add a mountinfo program to demonstrate statmount()/listmount()

Author: torvalds

fs/mount.h

@@ -8,15 +8,23 @@
 struct mnt_namespace {
 	struct ns_common	ns;
 	struct mount *	root;
-	struct rb_root		mounts; /* Protected by namespace_sem */
+	struct {
+		struct rb_root	mounts;		 /* Protected by namespace_sem */
+		struct rb_node	*mnt_last_node;	 /* last (rightmost) mount in the rbtree */
+		struct rb_node	*mnt_first_node; /* first (leftmost) mount in the rbtree */
+	};
 	struct user_namespace	*user_ns;
 	struct ucounts		*ucounts;
 	u64			seq;	/* Sequence number to prevent loops */
-	wait_queue_head_t poll;
+	union {
+		wait_queue_head_t	poll;
+		struct rcu_head		mnt_ns_rcu;
+	};
 	u64 event;
 	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;
 
@@ -150,22 +158,21 @@ static inline bool mnt_ns_attached(const struct mount *mnt)
 
 static inline void move_from_ns(struct mount *mnt, struct list_head *dt_list)
 {
+	struct mnt_namespace *ns = mnt->mnt_ns;
 	WARN_ON(!mnt_ns_attached(mnt));
-	rb_erase(&mnt->mnt_node, &mnt->mnt_ns->mounts);
+	if (ns->mnt_last_node == &mnt->mnt_node)
+		ns->mnt_last_node = rb_prev(&mnt->mnt_node);
+	if (ns->mnt_first_node == &mnt->mnt_node)
+		ns->mnt_first_node = rb_next(&mnt->mnt_node);
+	rb_erase(&mnt->mnt_node, &ns->mounts);
 	RB_CLEAR_NODE(&mnt->mnt_node);
 	list_add_tail(&mnt->mnt_list, dt_list);
 }
 
 bool has_locked_children(struct mount *mnt, struct dentry *dentry);
-struct mnt_namespace *__lookup_next_mnt_ns(struct mnt_namespace *mnt_ns, bool previous);
-static inline struct mnt_namespace *lookup_next_mnt_ns(struct mnt_namespace *mntns)
-{
-	return __lookup_next_mnt_ns(mntns, false);
-}
-static inline struct mnt_namespace *lookup_prev_mnt_ns(struct mnt_namespace *mntns)
-{
-	return __lookup_next_mnt_ns(mntns, true);
-}
+struct mnt_namespace *get_sequential_mnt_ns(struct mnt_namespace *mnt_ns,
+					    bool previous);
+
 static inline struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
 {
 	return container_of(ns, struct mnt_namespace, ns);