btrfs: sink argument tree to extent_read_full_page

The tree pointer can be safely read from the page's inode, use it and
drop the redundant argument.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -978,9 +978,7 @@ static int btree_writepages(struct address_space *mapping,
 
 static int btree_readpage(struct file *file, struct page *page)
 {
-	struct extent_io_tree *tree;
-	tree = &BTRFS_I(page->mapping->host)->io_tree;
-	return extent_read_full_page(tree, page, btree_get_extent, 0);
+	return extent_read_full_page(page, btree_get_extent, 0);
 }
 
 static int btree_releasepage(struct page *page, gfp_t gfp_flags)

fs/btrfs/extent_io.c

@@ -3361,15 +3361,14 @@ static int __extent_read_full_page(struct extent_io_tree *tree,
 	return ret;
 }
 
-int extent_read_full_page(struct extent_io_tree *tree, struct page *page,
-			    get_extent_t *get_extent, int mirror_num)
+int extent_read_full_page(struct page *page, get_extent_t *get_extent,
+			  int mirror_num)
 {
 	struct bio *bio = NULL;
 	unsigned long bio_flags = 0;
+	struct extent_io_tree *tree = &BTRFS_I(page->mapping->host)->io_tree;
 	int ret;
 
-	ASSERT(tree == &BTRFS_I(page->mapping->host)->io_tree);
-
 	ret = __extent_read_full_page(tree, page, get_extent, &bio, mirror_num,
 				      &bio_flags, 0);
 	if (bio)

fs/btrfs/extent_io.h

@@ -189,8 +189,8 @@ typedef struct extent_map *(get_extent_t)(struct btrfs_inode *inode,
 int try_release_extent_mapping(struct page *page, gfp_t mask);
 int try_release_extent_buffer(struct page *page);
 
-int extent_read_full_page(struct extent_io_tree *tree, struct page *page,
-			  get_extent_t *get_extent, int mirror_num);
+int extent_read_full_page(struct page *page, get_extent_t *get_extent,
+			  int mirror_num);
 int extent_write_full_page(struct page *page, struct writeback_control *wbc);
 int extent_write_locked_range(struct inode *inode, u64 start, u64 end,
 			      int mode);

fs/btrfs/inode.c

@@ -8268,9 +8268,7 @@ static int btrfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 int btrfs_readpage(struct file *file, struct page *page)
 {
-	struct extent_io_tree *tree;
-	tree = &BTRFS_I(page->mapping->host)->io_tree;
-	return extent_read_full_page(tree, page, btrfs_get_extent, 0);
+	return extent_read_full_page(page, btrfs_get_extent, 0);
 }
 
 static int btrfs_writepage(struct page *page, struct writeback_control *wbc)