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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Joel Jaeschke <joel.jaeschke@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.16 0256/1017] io_uring: terminate manual loop iterator loop correctly for non-vecs
Date:   Tue,  5 Apr 2022 09:19:29 +0200
Message-Id: <20220405070401.862362471@linuxfoundation.org>
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From: Jens Axboe <axboe@kernel.dk>

[ 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>
---
 fs/io_uring.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 974f6fb327e7..2d25c51b8a5d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3350,13 +3350,15 @@ 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;
 	}
-- 
2.34.1