io_uring: retry raw bdev writes if we hit -EOPNOTSUPP

For non-blocking issue, we set IOCB_NOWAIT in the kiocb. However, on a
raw block device, this yields an -EOPNOTSUPP return, as non-blocking
writes aren't supported. Turn this -EOPNOTSUPP into -EAGAIN, so we retry
from blocking context with IOCB_NOWAIT cleared.

Cc: stable@vger.kernel.org # 5.5
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2340,6 +2340,12 @@ static int io_write(struct io_kiocb *req, struct io_kiocb **nxt,
 			ret2 = call_write_iter(req->file, kiocb, &iter);
 		else
 			ret2 = loop_rw_iter(WRITE, req->file, kiocb, &iter);
+		/*
+		 * Raw bdev writes will -EOPNOTSUPP for IOCB_NOWAIT. Just
+		 * retry them without IOCB_NOWAIT.
+		 */
+		if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
+			ret2 = -EAGAIN;
 		if (!force_nonblock || ret2 != -EAGAIN) {
 			kiocb_done(kiocb, ret2, nxt, req->in_async);
 		} else {