btrfs: replace readpage_end_io_hook with direct calls

Don't call readpage_end_io_hook for the btree inode.  Instead of relying
on indirect calls to implement metadata buffer validation simply check
if the inode whose page we are processing equals the btree inode. If it
does call the necessary function.

This is an improvement in 2 directions:

1. We aren't paying the penalty of indirect calls in a post-speculation
   attacks world.

2. The function is now named more explicitly so it's obvious what's
   going on

This is in preparation to removing struct extent_io_ops altogether.
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 */
+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,
 					   u64 start, u64 len);
 noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,

fs/btrfs/disk-io.c

@@ -524,9 +524,9 @@ static int check_tree_block_fsid(struct extent_buffer *eb)
 	return 1;
 }
 
-static int btree_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
-				      u64 phy_offset, struct page *page,
-				      u64 start, u64 end, int mirror)
+int btrfs_validate_metadata_buffer(struct btrfs_io_bio *io_bio, u64 phy_offset,
+				   struct page *page, u64 start, u64 end,
+				   int mirror)
 {
 	u64 found_start;
 	int found_level;
@@ -4638,5 +4638,5 @@ static int btrfs_cleanup_transaction(struct btrfs_fs_info *fs_info)
 static const struct extent_io_ops btree_extent_io_ops = {
 	/* mandatory callbacks */
 	.submit_bio_hook = btree_submit_bio_hook,
-	.readpage_end_io_hook = btree_readpage_end_io_hook,
+	.readpage_end_io_hook = NULL
 };

fs/btrfs/disk-io.h

@@ -76,7 +76,9 @@ void btrfs_btree_balance_dirty(struct btrfs_fs_info *fs_info);
 void btrfs_btree_balance_dirty_nodelay(struct btrfs_fs_info *fs_info);
 void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 				 struct btrfs_root *root);
-
+int btrfs_validate_metadata_buffer(struct btrfs_io_bio *io_bio, u64 phy_offset,
+				   struct page *page, u64 start, u64 end,
+				   int mirror);
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 struct btrfs_root *btrfs_alloc_dummy_root(struct btrfs_fs_info *fs_info);
 #endif

fs/btrfs/extent_io.c

@@ -2851,9 +2851,12 @@ static void end_bio_extent_readpage(struct bio *bio)
 
 		mirror = io_bio->mirror_num;
 		if (likely(uptodate)) {
-			ret = tree->ops->readpage_end_io_hook(io_bio, offset,
-							      page, start, end,
-							      mirror);
+			if (data_inode)
+				ret = btrfs_verify_data_csum(io_bio, offset, page,
+							     start, end, mirror);
+			else
+				ret = btrfs_validate_metadata_buffer(io_bio,
+					offset, page, start, end, mirror);
 			if (ret)
 				uptodate = 0;
 			else

fs/btrfs/inode.c

@@ -2832,9 +2832,8 @@ static int check_data_csum(struct inode *inode, struct btrfs_io_bio *io_bio,
  * if there's a match, we allow the bio to finish.  If not, the code in
  * extent_io.c will try to find good copies for us.
  */
-static int btrfs_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
-				      u64 phy_offset, struct page *page,
-				      u64 start, u64 end, int mirror)
+int btrfs_verify_data_csum(struct btrfs_io_bio *io_bio, u64 phy_offset,
+			   struct page *page, u64 start, u64 end, int mirror)
 {
 	size_t offset = start - page_offset(page);
 	struct inode *inode = page->mapping->host;
@@ -10261,7 +10260,7 @@ 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,
-	.readpage_end_io_hook = btrfs_readpage_end_io_hook,
+	.readpage_end_io_hook = NULL
 };
 
 /*