btrfs: only clear EXTENT_LOCK bit in extent_invalidatepage

extent_invalidatepage() will try to clear all possible bits since it's
calling clear_extent_bit() with delete == 1.

This is currently fine, since for btree io tree, it only utilizes
EXTENT_LOCK bit.  But this could be a problem for later subpage support,
which will utilize extra io tree bit to represent additional info.

This patch will just convert that clear_extent_bit() to
unlock_extent_cached().

For current code since only EXTENT_LOCKED bit is utilized, this doesn't
change the behavior, but provides a much cleaner basis for incoming
subpage support.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -4431,14 +4431,22 @@ int extent_invalidatepage(struct extent_io_tree *tree,
 	u64 end = start + PAGE_SIZE - 1;
 	size_t blocksize = page->mapping->host->i_sb->s_blocksize;
 
+	/* This function is only called for the btree inode */
+	ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);
+
 	start += ALIGN(offset, blocksize);
 	if (start > end)
 		return 0;
 
 	lock_extent_bits(tree, start, end, &cached_state);
 	wait_on_page_writeback(page);
-	clear_extent_bit(tree, start, end, EXTENT_LOCKED | EXTENT_DELALLOC |
-			 EXTENT_DO_ACCOUNTING, 1, 1, &cached_state);
+
+	/*
+	 * Currently for btree io tree, only EXTENT_LOCKED is utilized,
+	 * so here we only need to unlock the extent range to free any
+	 * existing extent state.
+	 */
+	unlock_extent_cached(tree, start, end, &cached_state);
 	return 0;
 }