[PATCH 1/4] kernfs: Use VFS lookup context in d_revalidate()

[Shakeel Butt <shakeel.butt@linux.dev>]

The VFS supplies a stable parent inode and expected name to the
revalidation callback. Use them instead of recovering the same
information from mutable dentry fields.

Compare the name using its explicit length because it may point into the
pathname and need not be terminated at name->len. This also prepares the
callback for lockless operation.

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 fs/kernfs/dir.c | 39 +++++++++++++++++----------------------
 1 file changed, 17 insertions(+), 22 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 82bbaeb326aa..541bb5525437 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1171,23 +1171,19 @@ struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
 static int kernfs_dop_revalidate(struct inode *dir, const struct qstr *name,
 				 struct dentry *dentry, unsigned int flags)
 {
-	struct kernfs_node *kn, *parent;
+	struct kernfs_node *kn, *kn_parent;
+	struct kernfs_node *parent = dir->i_private;
 	struct kernfs_root *root;
+	const char *kn_name;
 
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
 
 	/* Negative hashed dentry? */
 	if (d_really_is_negative(dentry)) {
-		/* If the kernfs parent node has changed discard and
-		 * proceed to ->lookup.
-		 *
-		 * There's nothing special needed here when getting the
-		 * dentry parent, even if a concurrent rename is in
-		 * progress. That's because the dentry is negative so
-		 * it can only be the target of the rename and it will
-		 * be doing a d_move() not a replace. Consequently the
-		 * dentry d_parent won't change over the d_move().
+		/*
+		 * If the kernfs parent node has changed discard and proceed to
+		 * ->lookup.
 		 *
 		 * Also kernfs negative dentries transitioning from
 		 * negative to positive during revalidate won't happen
@@ -1195,14 +1191,11 @@ static int kernfs_dop_revalidate(struct inode *dir, const struct qstr *name,
 		 * changes and the lookup re-done so that a new positive
 		 * dentry can be properly created.
 		 */
-		root = kernfs_root_from_sb(dentry->d_sb);
+		root = kernfs_root(parent);
 		down_read(&root->kernfs_rwsem);
-		parent = kernfs_dentry_node(dentry->d_parent);
-		if (parent) {
-			if (kernfs_dir_changed(parent, dentry)) {
-				up_read(&root->kernfs_rwsem);
-				return 0;
-			}
+		if (kernfs_dir_changed(parent, dentry)) {
+			up_read(&root->kernfs_rwsem);
+			return 0;
 		}
 		up_read(&root->kernfs_rwsem);
 
@@ -1220,18 +1213,20 @@ static int kernfs_dop_revalidate(struct inode *dir, const struct qstr *name,
 	if (!kernfs_active(kn))
 		goto out_bad;
 
-	parent = kernfs_parent(kn);
+	kn_parent = kernfs_parent(kn);
 	/* The kernfs node has been moved? */
-	if (kernfs_dentry_node(dentry->d_parent) != parent)
+	if (parent != kn_parent)
 		goto out_bad;
 
 	/* The kernfs node has been renamed */
-	if (strcmp(dentry->d_name.name, kernfs_rcu_name(kn)) != 0)
+	kn_name = kernfs_rcu_name(kn);
+	if (name->len != strlen(kn_name) ||
+	    memcmp(name->name, kn_name, name->len))
 		goto out_bad;
 
 	/* The kernfs node has been moved to a different namespace */
-	if (parent && kernfs_ns_enabled(parent) &&
-	    kernfs_ns_id(kernfs_info(dentry->d_sb)->ns) != kernfs_ns_id(kn->ns))
+	if (kn_parent && kernfs_ns_enabled(kn_parent) &&
+	    kernfs_ns_id(kernfs_info(dir->i_sb)->ns) != kernfs_ns_id(kn->ns))
 		goto out_bad;
 
 	up_read(&root->kernfs_rwsem);
-- 
2.53.0-Meta