[PATCH] io_uring: fix short read/write with linked ops

[David Stevens <stevensd@chromium.org>]

From: David Stevens <stevensd@chromium.org>

When continuing a short read/write, account for any completed bytes when
calculating the operation's target length. The operation's actual
accumulated length is fixed up by kiocb_done, and the target and actual
lengths are then compared by __io_complete_rw_common. That function
already propagated the actual length to userspace, but the incorrect
target length was causing it to always cancel linked operations, even
with a successfully completed read/write.

Fixes: 227c0c9673d8 ("io_uring: internally retry short reads")
Signed-off-by: David Stevens <stevensd@chromium.org>
---
 io_uring/rw.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/io_uring/rw.c b/io_uring/rw.c
index 76ebcfebc9a6..aa9967a52dfd 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -706,13 +706,14 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
 	struct kiocb *kiocb = &rw->kiocb;
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
 	struct io_async_rw *io;
-	ssize_t ret, ret2;
+	ssize_t ret, ret2, target_len;
 	loff_t *ppos;
 
 	if (!req_has_async_data(req)) {
 		ret = io_import_iovec(READ, req, &iovec, s, issue_flags);
 		if (unlikely(ret < 0))
 			return ret;
+		target_len = iov_iter_count(&s->iter);
 	} else {
 		io = req->async_data;
 		s = &io->s;
@@ -733,6 +734,7 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
 		 * need to make this conditional.
 		 */
 		iov_iter_restore(&s->iter, &s->iter_state);
+		target_len = iov_iter_count(&s->iter) + io->bytes_done;
 		iovec = NULL;
 	}
 	ret = io_rw_init_file(req, FMODE_READ);
@@ -740,7 +742,7 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
 		kfree(iovec);
 		return ret;
 	}
-	req->cqe.res = iov_iter_count(&s->iter);
+	req->cqe.res = target_len;
 
 	if (force_nonblock) {
 		/* If the file doesn't support async, just async punt */
@@ -850,18 +852,20 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	struct iovec *iovec;
 	struct kiocb *kiocb = &rw->kiocb;
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
-	ssize_t ret, ret2;
+	ssize_t ret, ret2, target_len;
 	loff_t *ppos;
 
 	if (!req_has_async_data(req)) {
 		ret = io_import_iovec(WRITE, req, &iovec, s, issue_flags);
 		if (unlikely(ret < 0))
 			return ret;
+		target_len = iov_iter_count(&s->iter);
 	} else {
 		struct io_async_rw *io = req->async_data;
 
 		s = &io->s;
 		iov_iter_restore(&s->iter, &s->iter_state);
+		target_len = iov_iter_count(&s->iter) + io->bytes_done;
 		iovec = NULL;
 	}
 	ret = io_rw_init_file(req, FMODE_WRITE);
@@ -869,7 +873,7 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		kfree(iovec);
 		return ret;
 	}
-	req->cqe.res = iov_iter_count(&s->iter);
+	req->cqe.res = target_len;
 
 	if (force_nonblock) {
 		/* If the file doesn't support async, just async punt */
-- 
2.38.0.rc1.362.ged0d419d3c-goog