io_uring: catch -EIO from buffered issue request failure

-EIO bubbles up like -EAGAIN if we fail to allocate a request at the
lower level. Play it safe and treat it like -EAGAIN in terms of sync
retry, to avoid passing back an errant -EIO.

Catch some of these early for block based file, as non-mq devices
generally do not support NOWAIT. That saves us some overhead by
not first trying, then retrying from async context. We can go straight
to async punt instead.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2088,6 +2088,15 @@ static struct file *__io_file_get(struct io_submit_state *state, int fd)
 	return state->file;
 }
 
+static bool io_bdev_nowait(struct block_device *bdev)
+{
+#ifdef CONFIG_BLOCK
+	return !bdev || queue_is_mq(bdev_get_queue(bdev));
+#else
+	return true;
+#endif
+}
+
 /*
  * If we tracked the file through the SCM inflight mechanism, we could support
  * any file. For now, just ensure that anything potentially problematic is done
@@ -2097,10 +2106,19 @@ static bool io_file_supports_async(struct file *file, int rw)
 {
 	umode_t mode = file_inode(file)->i_mode;
 
-	if (S_ISBLK(mode) || S_ISCHR(mode) || S_ISSOCK(mode))
+	if (S_ISBLK(mode)) {
+		if (io_bdev_nowait(file->f_inode->i_bdev))
 			return true;
-	if (S_ISREG(mode) && file->f_op != &io_uring_fops)
+		return false;
+	}
+	if (S_ISCHR(mode) || S_ISSOCK(mode))
+		return true;
+	if (S_ISREG(mode)) {
+		if (io_bdev_nowait(file->f_inode->i_sb->s_bdev) &&
+		    file->f_op != &io_uring_fops)
 			return true;
+		return false;
+	}
 
 	/* any ->read/write should understand O_NONBLOCK */
 	if (file->f_flags & O_NONBLOCK)
@@ -2650,7 +2668,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
 	iov_count = iov_iter_count(&iter);
 	ret = rw_verify_area(READ, req->file, &kiocb->ki_pos, iov_count);
 	if (!ret) {
-		ssize_t ret2;
+		ssize_t ret2 = 0;
 
 		if (req->file->f_op->read_iter)
 			ret2 = call_read_iter(req->file, kiocb, &iter);
@@ -2658,7 +2676,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
 			ret2 = loop_rw_iter(READ, req->file, kiocb, &iter);
 
 		/* Catch -EAGAIN return for forced non-blocking submission */
-		if (!force_nonblock || ret2 != -EAGAIN) {
+		if (!force_nonblock || (ret2 != -EAGAIN && ret2 != -EIO)) {
 			kiocb_done(kiocb, ret2);
 		} else {
 copy_iov: