tracefs: Use d_inode() helper function to get the dentry inode

Instead of referencing the inode from a dentry via dentry->d_inode, use
the helper function d_inode(dentry) instead. This is the considered the
correct way to access it.
Reported-by: Christian Brauner <christian.brauner@ubuntu.com>
Reported: https://lore.kernel.org/all/20211208104454.nhxyvmmn6d2qhpwl@wittgenstein/Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

fs/tracefs/inode.c

@@ -109,12 +109,12 @@ static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
 	 * also the directory that is being deleted.
 	 */
 	inode_unlock(inode);
-	inode_unlock(dentry->d_inode);
+	inode_unlock(d_inode(dentry));
 
 	ret = tracefs_ops.rmdir(name);
 
 	inode_lock_nested(inode, I_MUTEX_PARENT);
-	inode_lock(dentry->d_inode);
+	inode_lock(d_inode(dentry));
 
 	kfree(name);
 
@@ -212,7 +212,7 @@ static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
 static int tracefs_apply_options(struct super_block *sb)
 {
 	struct tracefs_fs_info *fsi = sb->s_fs_info;
-	struct inode *inode = sb->s_root->d_inode;
+	struct inode *inode = d_inode(sb->s_root);
 	struct tracefs_mount_opts *opts = &fsi->mount_opts;
 
 	inode->i_mode &= ~S_IALLUGO;
@@ -331,18 +331,18 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
 	if (!parent)
 		parent = tracefs_mount->mnt_root;
 
-	inode_lock(parent->d_inode);
-	if (unlikely(IS_DEADDIR(parent->d_inode)))
+	inode_lock(d_inode(parent));
+	if (unlikely(IS_DEADDIR(d_inode(parent))))
 		dentry = ERR_PTR(-ENOENT);
 	else
 		dentry = lookup_one_len(name, parent, strlen(name));
-	if (!IS_ERR(dentry) && dentry->d_inode) {
+	if (!IS_ERR(dentry) && d_inode(dentry)) {
 		dput(dentry);
 		dentry = ERR_PTR(-EEXIST);
 	}
 
 	if (IS_ERR(dentry)) {
-		inode_unlock(parent->d_inode);
+		inode_unlock(d_inode(parent));
 		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 	}
 
@@ -351,7 +351,7 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
 
 static struct dentry *failed_creating(struct dentry *dentry)
 {
-	inode_unlock(dentry->d_parent->d_inode);
+	inode_unlock(d_inode(dentry->d_parent));
 	dput(dentry);
 	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 	return NULL;
@@ -359,7 +359,7 @@ static struct dentry *failed_creating(struct dentry *dentry)
 
 static struct dentry *end_creating(struct dentry *dentry)
 {
-	inode_unlock(dentry->d_parent->d_inode);
+	inode_unlock(d_inode(dentry->d_parent));
 	return dentry;
 }
 
@@ -415,7 +415,7 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
 	inode->i_fop = fops ? fops : &tracefs_file_operations;
 	inode->i_private = data;
 	d_instantiate(dentry, inode);
-	fsnotify_create(dentry->d_parent->d_inode, dentry);
+	fsnotify_create(d_inode(dentry->d_parent), dentry);
 	return end_creating(dentry);
 }
 
@@ -440,8 +440,8 @@ static struct dentry *__create_dir(const char *name, struct dentry *parent,
 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
 	inc_nlink(inode);
 	d_instantiate(dentry, inode);
-	inc_nlink(dentry->d_parent->d_inode);
-	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
+	inc_nlink(d_inode(dentry->d_parent));
+	fsnotify_mkdir(d_inode(dentry->d_parent), dentry);
 	return end_creating(dentry);
 }