block: don't silently ignore metadata for sync read/write

The block fops don't try to handle metadata for synchronous requests,
probably because the completion handler looks at dio->iocb which is not
valid for synchronous requests.

But silently ignoring metadata (or warning in case of
__blkdev_direct_IO_simple) is a really bad idea as that can cause
silent data corruption if a user ever shows up.

Instead simply handle metadata for synchronous requests as the completion
handler can simply check for bio_integrity() as the block layer default
integrity will already be freed at this point, and thus bio_integrity()
will only return true for user mapped integrity.

Fixes: 3d8b5a2 ("block: add support to pass user meta buffer")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/20250819082517.2038819-3-hch@lst.de
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Christoph Hellwig

block/fops.c

@@ -55,7 +55,6 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
 	struct bio bio;
 	ssize_t ret;
 
-	WARN_ON_ONCE(iocb->ki_flags & IOCB_HAS_METADATA);
 	if (nr_pages <= DIO_INLINE_BIO_VECS)
 		vecs = inline_vecs;
 	else {
@@ -132,7 +131,7 @@ static void blkdev_bio_end_io(struct bio *bio)
 	if (bio->bi_status && !dio->bio.bi_status)
 		dio->bio.bi_status = bio->bi_status;
 
-	if (!is_sync && (dio->iocb->ki_flags & IOCB_HAS_METADATA))
+	if (bio_integrity(bio))
 		bio_integrity_unmap_user(bio);
 
 	if (atomic_dec_and_test(&dio->ref)) {
@@ -234,7 +233,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 			}
 			bio->bi_opf |= REQ_NOWAIT;
 		}
-		if (!is_sync && (iocb->ki_flags & IOCB_HAS_METADATA)) {
+		if (iocb->ki_flags & IOCB_HAS_METADATA) {
 			ret = bio_integrity_map_iter(bio, iocb->private);
 			if (unlikely(ret))
 				goto fail;
@@ -302,7 +301,7 @@ static void blkdev_bio_end_io_async(struct bio *bio)
 		ret = blk_status_to_errno(bio->bi_status);
 	}
 
-	if (iocb->ki_flags & IOCB_HAS_METADATA)
+	if (bio_integrity(bio))
 		bio_integrity_unmap_user(bio);
 
 	iocb->ki_complete(iocb, ret);
@@ -423,7 +422,8 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	}
 
 	nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS + 1);
-	if (likely(nr_pages <= BIO_MAX_VECS)) {
+	if (likely(nr_pages <= BIO_MAX_VECS &&
+		   !(iocb->ki_flags & IOCB_HAS_METADATA))) {
 		if (is_sync_kiocb(iocb))
 			return __blkdev_direct_IO_simple(iocb, iter, bdev,
 							nr_pages);