lock_rename_child() (for ksmbd folks)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-lock_rename_child' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs into ksmbd-for-next

lock_rename_child() (for ksmbd folks)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/internal.h

@@ -59,8 +59,6 @@ extern int finish_clean_context(struct fs_context *fc);
  */
 extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
 			   struct path *path, struct path *root);
-extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
-			   const char *, unsigned int, struct path *);
 int do_rmdir(int dfd, struct filename *name);
 int do_unlinkat(int dfd, struct filename *name);
 int may_linkat(struct mnt_idmap *idmap, const struct path *link);

fs/ksmbd/vfs.c

@@ -19,8 +19,6 @@
 #include <linux/sched/xacct.h>
 #include <linux/crc32c.h>
 
-#include "../internal.h"	/* for vfs_path_lookup */
-
 #include "glob.h"
 #include "oplock.h"
 #include "connection.h"

fs/namei.c

@@ -2980,20 +2980,10 @@ static inline int may_create(struct mnt_idmap *idmap,
 	return inode_permission(idmap, dir, MAY_WRITE | MAY_EXEC);
 }
 
-/*
+static struct dentry *lock_two_directories(struct dentry *p1, struct dentry *p2)
- * p1 and p2 should be directories on the same fs.
- */
-struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
 {
 	struct dentry *p;
 
-	if (p1 == p2) {
-		inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
-		return NULL;
-	}
-
-	mutex_lock(&p1->d_sb->s_vfs_rename_mutex);
-
 	p = d_ancestor(p2, p1);
 	if (p) {
 		inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
@@ -3012,8 +3002,64 @@ struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
 	inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2);
 	return NULL;
 }
+
+/*
+ * p1 and p2 should be directories on the same fs.
+ */
+struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
+{
+	if (p1 == p2) {
+		inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
+		return NULL;
+	}
+
+	mutex_lock(&p1->d_sb->s_vfs_rename_mutex);
+	return lock_two_directories(p1, p2);
+}
 EXPORT_SYMBOL(lock_rename);
 
+/*
+ * c1 and p2 should be on the same fs.
+ */
+struct dentry *lock_rename_child(struct dentry *c1, struct dentry *p2)
+{
+	if (READ_ONCE(c1->d_parent) == p2) {
+		/*
+		 * hopefully won't need to touch ->s_vfs_rename_mutex at all.
+		 */
+		inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
+		/*
+		 * now that p2 is locked, nobody can move in or out of it,
+		 * so the test below is safe.
+		 */
+		if (likely(c1->d_parent == p2))
+			return NULL;
+
+		/*
+		 * c1 got moved out of p2 while we'd been taking locks;
+		 * unlock and fall back to slow case.
+		 */
+		inode_unlock(p2->d_inode);
+	}
+
+	mutex_lock(&c1->d_sb->s_vfs_rename_mutex);
+	/*
+	 * nobody can move out of any directories on this fs.
+	 */
+	if (likely(c1->d_parent != p2))
+		return lock_two_directories(c1->d_parent, p2);
+
+	/*
+	 * c1 got moved into p2 while we were taking locks;
+	 * we need p2 locked and ->s_vfs_rename_mutex unlocked,
+	 * for consistency with lock_rename().
+	 */
+	inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
+	mutex_unlock(&c1->d_sb->s_vfs_rename_mutex);
+	return NULL;
+}
+EXPORT_SYMBOL(lock_rename_child);
+
 void unlock_rename(struct dentry *p1, struct dentry *p2)
 {
 	inode_unlock(p1->d_inode);

include/linux/namei.h

@@ -63,6 +63,8 @@ extern struct dentry *kern_path_create(int, const char *, struct path *, unsigne
 extern struct dentry *user_path_create(int, const char __user *, struct path *, unsigned int);
 extern void done_path_create(struct path *, struct dentry *);
 extern struct dentry *kern_path_locked(const char *, struct path *);
+int vfs_path_lookup(struct dentry *, struct vfsmount *, const char *,
+		    unsigned int, struct path *);
 
 extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int);
 extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
@@ -81,6 +83,7 @@ extern int follow_down(struct path *path, unsigned int flags);
 extern int follow_up(struct path *);
 
 extern struct dentry *lock_rename(struct dentry *, struct dentry *);
+extern struct dentry *lock_rename_child(struct dentry *, struct dentry *);
 extern void unlock_rename(struct dentry *, struct dentry *);
 
 extern int __must_check nd_jump_link(const struct path *path);