hi,
On 6/15/20 3:24 AM, Xiaoguang Wang wrote:
In io_complete_rw_iopoll(), stores to io_kiocb's result and iopoll
completed are two independent store operations, to ensure that once
iopoll_completed is ture and then req->result must been perceived by
the cpu executing io_do_iopoll(), proper memory barrier should be used.
And in io_do_iopoll(), we check whether req->result is EAGAIN, if it is,
we'll need to issue this io request using io-wq again. In order to just
issue a single smp_rmb() on the completion side, move the re-submit work
to io_iopoll_complete().
Did you actually test this one?
I only run test cases in liburing/test in a vm.
@@ -1736,11 +1748,20 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
{
struct req_batch rb;
struct io_kiocb *req;
+ LIST_HEAD(again);
+
+ /* order with ->result store in io_complete_rw_iopoll() */
+ smp_rmb();
rb.to_free = rb.need_iter = 0;
while (!list_empty(done)) {
int cflags = 0;
+ if (READ_ONCE(req->result) == -EAGAIN) {
+ req->iopoll_completed = 0;
+ list_move_tail(&req->list, &again);
+ continue;
+ }
req = list_first_entry(done, struct io_kiocb, list);
list_del(&req->list);
You're using 'req' here before you initialize it...
Sorry, next time when I submit patches, I'll construct test cases which
will cover my codes changes.
Regards,
Xiaoguang Wang
