[PATCH for-next v2 1/2] io_uring/rw: fix unexpected link breakage

[Pavel Begunkov <asml.silence@gmail.com>]

req->cqe.res is set in io_read() to the amount of bytes left to be done,
which is used to figure out whether to fail a read or not. However,
io_read() may do another without returning, and we stash the previous
value into ->bytes_done but forget to update cqe.res. Then we ask a read
to do strictly less than cqe.res but expect the return to be exactly
cqe.res.

Fix the bug by updating cqe.res for retries.

Cc: stable@vger.kernel.org
Reported-and-Tested-by: Beld Zhang <beldzhang@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rw.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/io_uring/rw.c b/io_uring/rw.c
index 59c92a4616b8..ed14322aadb9 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -793,6 +793,7 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
 			return -EAGAIN;
 		}
 
+		req->cqe.res = iov_iter_count(&s->iter);
 		/*
 		 * Now retry read with the IOCB_WAITQ parts set in the iocb. If
 		 * we get -EIOCBQUEUED, then we'll get a notification when the
-- 
2.37.2