erofs: set fileio bio failed in short read case

For file-backed mount, IO requests are handled by vfs_iocb_iter_read().
However, it can be interrupted by SIGKILL, returning the number of
bytes actually copied. Unused folios in bio are unexpectedly marked
as uptodate.

  vfs_read
    filemap_read
      filemap_get_pages
        filemap_readahead
          erofs_fileio_readahead
            erofs_fileio_rq_submit
              vfs_iocb_iter_read
                filemap_read
                  filemap_get_pages  <= detect signal
              erofs_fileio_ki_complete  <= set all folios uptodate

This patch addresses this by setting short read bio with an error
directly.

Fixes: bc804a8 ("erofs: handle end of filesystem properly for file-backed mounts")
Reported-by: chenguanyou <[email protected]>
Signed-off-by: Yunlei He <[email protected]>
Signed-off-by: Sheng Yong <[email protected]>
Reviewed-by: Gao Xiang <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Gao Xiang <[email protected]>

Author: Sheng Yong

fs/erofs/fileio.c

@@ -25,10 +25,8 @@ static void erofs_fileio_ki_complete(struct kiocb *iocb, long ret)
 			container_of(iocb, struct erofs_fileio_rq, iocb);
 	struct folio_iter fi;
 
-	if (ret >= 0 && ret != rq->bio.bi_iter.bi_size) {
-		bio_advance(&rq->bio, ret);
-		zero_fill_bio(&rq->bio);
-	}
+	if (ret >= 0 && ret != rq->bio.bi_iter.bi_size)
+		ret = -EIO;
 	if (!rq->bio.bi_end_io) {
 		bio_for_each_folio_all(fi, &rq->bio) {
 			DBG_BUGON(folio_test_uptodate(fi.folio));