btrfs: stop calling submit_bio_hook for data inodes

Instead export and rename the function to btrfs_submit_data_bio and
call it directly in submit_one_bio. This avoids paying the cost for
speculative attacks mitigations and improves code readability.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -2969,6 +2969,8 @@ void btrfs_inode_safe_disk_i_size_write(struct inode *inode, u64 new_i_size);
 u64 btrfs_file_extent_end(const struct btrfs_path *path);
 
 /* inode.c */
+blk_status_t btrfs_submit_data_bio(struct inode *inode, struct bio *bio,
+				   int mirror_num, unsigned long bio_flags);
 int btrfs_verify_data_csum(struct btrfs_io_bio *io_bio, u64 phy_offset,
 			   struct page *page, u64 start, u64 end, int mirror);
 struct extent_map *btrfs_get_extent_fiemap(struct btrfs_inode *inode,

fs/btrfs/extent_io.c

@@ -168,8 +168,12 @@ int __must_check submit_one_bio(struct bio *bio, int mirror_num,
 
 	bio->bi_private = NULL;
 
-	ret = tree->ops->submit_bio_hook(tree->private_data, bio, mirror_num,
+	if (is_data_inode(tree->private_data))
+		ret = btrfs_submit_data_bio(tree->private_data, bio, mirror_num,
 					    bio_flags);
+	else
+		ret = tree->ops->submit_bio_hook(tree->private_data, bio,
+						 mirror_num, bio_flags);
 
 	return blk_status_to_errno(ret);
 }
@@ -2879,7 +2883,7 @@ static void end_bio_extent_readpage(struct bio *bio)
 			if (!btrfs_submit_read_repair(inode, bio, offset, page,
 						start - page_offset(page),
 						start, end, mirror,
-						tree->ops->submit_bio_hook)) {
+						btrfs_submit_data_bio)) {
 				uptodate = !bio->bi_status;
 				offset += len;
 				continue;

fs/btrfs/inode.c

@@ -2184,9 +2184,8 @@ static blk_status_t btrfs_submit_bio_start(void *private_data, struct bio *bio,
  *
  *    c-3) otherwise:			async submit
  */
-static blk_status_t btrfs_submit_bio_hook(struct inode *inode, struct bio *bio,
-					  int mirror_num,
-					  unsigned long bio_flags)
+blk_status_t btrfs_submit_data_bio(struct inode *inode, struct bio *bio,
+				   int mirror_num, unsigned long bio_flags)
 
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
@@ -10258,8 +10257,7 @@ static const struct file_operations btrfs_dir_file_operations = {
 };
 
 static const struct extent_io_ops btrfs_extent_io_ops = {
-	/* mandatory callbacks */
-	.submit_bio_hook = btrfs_submit_bio_hook,
+	.submit_bio_hook = NULL
 };
 
 /*