ext4: store cookie in private data

Store the cookie to detect concurrent seeks on directories in
file->private_data.

Link: https://lore.kernel.org/r/20240830-vfs-file-f_version-v1-11-6d3e4816aa7b@kernel.org
Acked-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/ext4/dir.c

@@ -133,6 +133,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
 	struct super_block *sb = inode->i_sb;
 	struct buffer_head *bh = NULL;
 	struct fscrypt_str fstr = FSTR_INIT(NULL, 0);
+	struct dir_private_info *info = file->private_data;
 
 	err = fscrypt_prepare_readdir(inode);
 	if (err)
@@ -229,7 +230,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
 		 * readdir(2), then we might be pointing to an invalid
 		 * dirent right now.  Scan from the start of the block
 		 * to make sure. */
-		if (!inode_eq_iversion(inode, file->f_version)) {
+		if (!inode_eq_iversion(inode, info->cookie)) {
 			for (i = 0; i < sb->s_blocksize && i < offset; ) {
 				de = (struct ext4_dir_entry_2 *)
 					(bh->b_data + i);
@@ -249,7 +250,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
 			offset = i;
 			ctx->pos = (ctx->pos & ~(sb->s_blocksize - 1))
 				| offset;
-			file->f_version = inode_query_iversion(inode);
+			info->cookie = inode_query_iversion(inode);
 		}
 
 		while (ctx->pos < inode->i_size
@@ -384,6 +385,7 @@ static inline loff_t ext4_get_htree_eof(struct file *filp)
 static loff_t ext4_dir_llseek(struct file *file, loff_t offset, int whence)
 {
 	struct inode *inode = file->f_mapping->host;
+	struct dir_private_info *info = file->private_data;
 	int dx_dir = is_dx_dir(inode);
 	loff_t ret, htree_max = ext4_get_htree_eof(file);
 
@@ -392,7 +394,7 @@ static loff_t ext4_dir_llseek(struct file *file, loff_t offset, int whence)
 						    htree_max, htree_max);
 	else
 		ret = ext4_llseek(file, offset, whence);
-	file->f_version = inode_peek_iversion(inode) - 1;
+	info->cookie = inode_peek_iversion(inode) - 1;
 	return ret;
 }
 
@@ -429,18 +431,15 @@ static void free_rb_tree_fname(struct rb_root *root)
 	*root = RB_ROOT;
 }
 
-
+static void ext4_htree_init_dir_info(struct file *filp, loff_t pos)
-static struct dir_private_info *ext4_htree_create_dir_info(struct file *filp,
-							   loff_t pos)
 {
-	struct dir_private_info *p;
+	struct dir_private_info *p = filp->private_data;
 
-	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (is_dx_dir(file_inode(filp)) && !p->initialized) {
-	if (!p)
-		return NULL;
 		p->curr_hash = pos2maj_hash(filp, pos);
 		p->curr_minor_hash = pos2min_hash(filp, pos);
-	return p;
+		p->initialized = true;
+	}
 }
 
 void ext4_htree_free_dir_info(struct dir_private_info *p)
@@ -552,12 +551,7 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
 	struct fname *fname;
 	int ret = 0;
 
-	if (!info) {
+	ext4_htree_init_dir_info(file, ctx->pos);
-		info = ext4_htree_create_dir_info(file, ctx->pos);
-		if (!info)
-			return -ENOMEM;
-		file->private_data = info;
-	}
 
 	if (ctx->pos == ext4_get_htree_eof(file))
 		return 0;	/* EOF */
@@ -590,10 +584,10 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
 		 * cached entries.
 		 */
 		if ((!info->curr_node) ||
-		    !inode_eq_iversion(inode, file->f_version)) {
+		    !inode_eq_iversion(inode, info->cookie)) {
 			info->curr_node = NULL;
 			free_rb_tree_fname(&info->root);
-			file->f_version = inode_query_iversion(inode);
+			info->cookie = inode_query_iversion(inode);
 			ret = ext4_htree_fill_tree(file, info->curr_hash,
 						   info->curr_minor_hash,
 						   &info->next_hash);
@@ -664,7 +658,19 @@ int ext4_check_all_de(struct inode *dir, struct buffer_head *bh, void *buf,
 	return 0;
 }
 
+static int ext4_dir_open(struct inode *inode, struct file *file)
+{
+	struct dir_private_info *info;
+
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+	file->private_data = info;
+	return 0;
+}
+
 const struct file_operations ext4_dir_operations = {
+	.open		= ext4_dir_open,
 	.llseek		= ext4_dir_llseek,
 	.read		= generic_read_dir,
 	.iterate_shared	= ext4_readdir,

fs/ext4/ext4.h

@@ -2553,6 +2553,8 @@ struct dir_private_info {
 	__u32		curr_hash;
 	__u32		curr_minor_hash;
 	__u32		next_hash;
+	u64		cookie;
+	bool		initialized;
 };
 
 /* calculate the first block number of the group */

fs/ext4/inline.c

@@ -1460,6 +1460,7 @@ int ext4_read_inline_dir(struct file *file,
 	struct ext4_iloc iloc;
 	void *dir_buf = NULL;
 	int dotdot_offset, dotdot_size, extra_offset, extra_size;
+	struct dir_private_info *info = file->private_data;
 
 	ret = ext4_get_inode_loc(inode, &iloc);
 	if (ret)
@@ -1503,12 +1504,12 @@ int ext4_read_inline_dir(struct file *file,
 	extra_size = extra_offset + inline_size;
 
 	/*
-	 * If the version has changed since the last call to
+	 * If the cookie has changed since the last call to
 	 * readdir(2), then we might be pointing to an invalid
 	 * dirent right now.  Scan from the start of the inline
 	 * dir to make sure.
 	 */
-	if (!inode_eq_iversion(inode, file->f_version)) {
+	if (!inode_eq_iversion(inode, info->cookie)) {
 		for (i = 0; i < extra_size && i < offset;) {
 			/*
 			 * "." is with offset 0 and
@@ -1540,7 +1541,7 @@ int ext4_read_inline_dir(struct file *file,
 		}
 		offset = i;
 		ctx->pos = offset;
-		file->f_version = inode_query_iversion(inode);
+		info->cookie = inode_query_iversion(inode);
 	}
 
 	while (ctx->pos < extra_size) {