[PATCH] loop: fallback to buffered IO in case of dio submission failure

[Ming Lei <ming.lei@xxxxxxxxxx>]

Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 drivers/block/loop.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7bf4686af774..2fa15933860d 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -562,6 +562,14 @@ static void lo_rw_aio_complete(struct kiocb *iocb, long ret, long ret2)
 	lo_rw_aio_do_completion(cmd);
 }
 
+static inline int lo_call_backing_rw_iter(struct file *file,
+		struct kiocb *iocb, struct iov_iter *iter, bool rw)
+{
+	if (rw == WRITE)
+		return call_write_iter(file, iocb, iter);
+	return call_read_iter(file, iocb, iter);
+}
+
 static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 		     loff_t pos, bool rw)
 {
@@ -619,15 +627,18 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	cmd->iocb.ki_flags = IOCB_DIRECT;
 	cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
 
-	if (rw == WRITE)
-		ret = call_write_iter(file, &cmd->iocb, &iter);
-	else
-		ret = call_read_iter(file, &cmd->iocb, &iter);
+	ret = lo_call_backing_rw_iter(file, &cmd->iocb, &iter, rw);
 
 	lo_rw_aio_do_completion(cmd);
 
-	if (ret != -EIOCBQUEUED)
+	if (ret >= 0) {
 		cmd->iocb.ki_complete(&cmd->iocb, ret, 0);
+	} else if (ret != -EIOCBQUEUED) {
+		/* fallback to buffered IO */
+		cmd->iocb.ki_flags = 0;
+		cmd->ret = lo_call_backing_rw_iter(file, &cmd->iocb, &iter, rw);
+		lo_rw_aio_do_completion(cmd);
+	}
 	return 0;
 }
 
-- 
2.31.1