kernfs: switch global kernfs_rename_lock to per-fs lock

The kernfs implementation has big lock granularity(kernfs_rename_lock) so
every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the lock.

This patch switches the global kernfs_rename_lock to per-fs lock, which
put the rwlock into kernfs_root.

Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20250415153659.14950-3-alexjlzheng@tencent.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 11 insertions, 4 deletions

diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 24e9514565ac..6061b6f70d2a 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -19,8 +19,6 @@
 #include <linux/kernfs.h>
 #include <linux/fs_context.h>
 
-extern rwlock_t kernfs_rename_lock;
-
 struct kernfs_iattrs {
 	kuid_t			ia_uid;
 	kgid_t			ia_gid;
@@ -53,6 +51,9 @@ struct kernfs_root {
 	struct rw_semaphore	kernfs_iattr_rwsem;
 	struct rw_semaphore	kernfs_supers_rwsem;
 
+	/* kn->parent and kn->name */
+	rwlock_t		kernfs_rename_lock;
+
 	struct rcu_head		rcu;
 };
 
@@ -108,6 +109,11 @@ static inline bool kernfs_root_is_locked(const struct kernfs_node *kn)
 	return lockdep_is_held(&kernfs_root(kn)->kernfs_rwsem);
 }
 
+static inline bool kernfs_rename_is_locked(const struct kernfs_node *kn)
+{
+	return lockdep_is_held(&kernfs_root(kn)->kernfs_rename_lock);
+}
+
 static inline const char *kernfs_rcu_name(const struct kernfs_node *kn)
 {
 	return rcu_dereference_check(kn->name, kernfs_root_is_locked(kn));
@@ -118,14 +124,15 @@ static inline struct kernfs_node *kernfs_parent(const struct kernfs_node *kn)
 	/*
 	 * The kernfs_node::__parent remains valid within a RCU section. The kn
 	 * can be reparented (and renamed) which changes the entry. This can be
-	 * avoided by locking kernfs_root::kernfs_rwsem or kernfs_rename_lock.
+	 * avoided by locking kernfs_root::kernfs_rwsem or
+	 * kernfs_root::kernfs_rename_lock.
 	 * Both locks can be used to obtain a reference on __parent. Once the
 	 * reference count reaches 0 then the node is about to be freed
 	 * and can not be renamed (or become a different parent) anymore.
 	 */
 	return rcu_dereference_check(kn->__parent,
 				     kernfs_root_is_locked(kn) ||
-				     lockdep_is_held(&kernfs_rename_lock) ||
+				     kernfs_rename_is_locked(kn) ||
 				     !atomic_read(&kn->count));
 }