From: Jens Axboe <axboe@kernel.dk>
Date: Fri, 18 Mar 2022 17:28:13 +0000 (-0600)
Subject: io_uring: terminate manual loop iterator loop correctly for non-vecs
X-Git-Tag: v6.1-rc5~1632^2~19
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=5e929367468c8f97cd1ffb0417316cecfebef94b;p=platform%2Fkernel%2Flinux-starfive.git

io_uring: terminate manual loop iterator loop correctly for non-vecs

The fix for not advancing the iterator if we're using fixed buffers is
broken in that it can hit a condition where we don't terminate the loop.
This results in io-wq looping forever, asking to read (or write) 0 bytes
for every subsequent loop.

Reported-by: Joel Jaeschke <joel.jaeschke@gmail.com>
Link: https://github.com/axboe/liburing/issues/549
Fixes: 16c8d2df7ec0 ("io_uring: ensure symmetry in handling iter types in loop_rw_iter()")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2d6ab73..5fa7363 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3612,13 +3612,15 @@ static ssize_t loop_rw_iter(int rw, struct io_kiocb *req, struct iov_iter *iter)
 				ret = nr;
 			break;
 		}
+		ret += nr;
 		if (!iov_iter_is_bvec(iter)) {
 			iov_iter_advance(iter, nr);
 		} else {
-			req->rw.len -= nr;
 			req->rw.addr += nr;
+			req->rw.len -= nr;
+			if (!req->rw.len)
+				break;
 		}
-		ret += nr;
 		if (nr != iovec.iov_len)
 			break;
 	}