Btrfs: mark mapping with error flag to report errors to userspace

According to commit 865ffef3797da2cac85b3354b5b6050dc9660978
(fs: fix fsync() error reporting),
it's not stable to just check error pages because pages can be
truncated or invalidated, we should also mark mapping with error
flag so that a later fsync can catch the error.

Signed-off-by: Liu Bo <[e-mail]>
Signed-off-by: Chris Mason <[e-mail]>

fs/btrfs/extent_io.c

···
 	if (!uptodate) {
 		ClearPageUptodate(page);
 		SetPageError(page);
+		ret = ret < 0 ? ret : -EIO;
+		mapping_set_error(page->mapping, ret);
 	}
 	return 0;
 }