io_uring/rw: fix short rw error handling

We have a couple of problems, first reports of unexpected link breakage
for reads when cqe->res indicates that the IO was done in full. The
reason here is partial IO with retries.

TL;DR; we compare the result in __io_complete_rw_common() against
req->cqe.res, but req->cqe.res doesn't store the full length but rather
the length left to be done. So, when we pass the full corrected result
via kiocb_done() -> __io_complete_rw_common(), it fails.

The second problem is that we don't try to correct res in
io_complete_rw(), which, for instance, might be a problem for O_DIRECT
but when a prefix of data was cached in the page cache. We also
definitely don't want to pass a corrected result into io_rw_done().

The fix here is to leave __io_complete_rw_common() alone, always pass
not corrected result into it and fix it up as the last step just before
actually finishing the I/O.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://github.com/axboe/liburing/issues/643
Reported-by: Beld Zhang <beldzhang@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/rw.c b/io_uring/rw.c
index 1babd77..1e18a44 100644 (file)
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -206,6 +206,20 @@ static bool __io_complete_rw_common(struct io_kiocb *req, long res)
        return false;
 }
 
+static inline unsigned io_fixup_rw_res(struct io_kiocb *req, unsigned res)
+{
+       struct io_async_rw *io = req->async_data;
+
+       /* add previously done IO, if any */
+       if (req_has_async_data(req) && io->bytes_done > 0) {
+               if (res < 0)
+                       res = io->bytes_done;
+               else
+                       res += io->bytes_done;
+       }
+       return res;
+}
+
 static void io_complete_rw(struct kiocb *kiocb, long res)
 {
        struct io_rw *rw = container_of(kiocb, struct io_rw, kiocb);
@@ -213,7 +227,7 @@ static void io_complete_rw(struct kiocb *kiocb, long res)
 
        if (__io_complete_rw_common(req, res))
                return;
-       io_req_set_res(req, res, 0);
+       io_req_set_res(req, io_fixup_rw_res(req, res), 0);
        req->io_task_work.func = io_req_task_complete;
        io_req_task_work_add(req);
 }
@@ -240,22 +254,14 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res)
 static int kiocb_done(struct io_kiocb *req, ssize_t ret,
                       unsigned int issue_flags)
 {
-       struct io_async_rw *io = req->async_data;
        struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
-
-       /* add previously done IO, if any */
-       if (req_has_async_data(req) && io->bytes_done > 0) {
-               if (ret < 0)
-                       ret = io->bytes_done;
-               else
-                       ret += io->bytes_done;
-       }
+       unsigned final_ret = io_fixup_rw_res(req, ret);
 
        if (req->flags & REQ_F_CUR_POS)
                req->file->f_pos = rw->kiocb.ki_pos;
        if (ret >= 0 && (rw->kiocb.ki_complete == io_complete_rw)) {
                if (!__io_complete_rw_common(req, ret)) {
-                       io_req_set_res(req, req->cqe.res,
+                       io_req_set_res(req, final_ret,
                                       io_put_kbuf(req, issue_flags));
                        return IOU_OK;
                }
@@ -268,7 +274,7 @@ static int kiocb_done(struct io_kiocb *req, ssize_t ret,
                if (io_resubmit_prep(req))
                        io_req_task_queue_reissue(req);
                else
-                       io_req_task_queue_fail(req, ret);
+                       io_req_task_queue_fail(req, final_ret);
        }
        return IOU_ISSUE_SKIP_COMPLETE;
 }