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

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit 5e929367468c8f97cd1ffb0417316cecfebef94b ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 109dda45102112799e507a65e375ebb096d3ae49)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 70e85f64dc3897f1c91bac25870137cea5086bf8..ec0b50940405f9c7b4bef00d9eca91dde370ff6d 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3319,13 +3319,15 @@ 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;
        }