iomap: fix submission side handling of completion side errors

[ Upstream commit 4ad357e ]

The "if (dio->error)" in iomap_dio_bio_iter exists to stop submitting
more bios when a completion already return an error.  Commit cfe057f
("iomap_dio_actor(): fix iov_iter bugs") made it revert the iov by
"copied", which is very wrong given that we've already consumed that
range and submitted a bio for it.

Fixes: cfe057f ("iomap_dio_actor(): fix iov_iter bugs")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Christoph Hellwig

fs/iomap/direct-io.c

@@ -381,9 +381,13 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 	nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
 	do {
 		size_t n;
-		if (dio->error) {
-			iov_iter_revert(dio->submit.iter, copied);
-			copied = ret = 0;
+
+		/*
+		 * If completions already occurred and reported errors, give up now and
+		 * don't bother submitting more bios.
+		 */
+		if (unlikely(data_race(dio->error))) {
+			ret = 0;
 			goto out;
 		}