io_uring: simplify iopoll reissuing

Don't stash -EAGAIN'ed iopoll requests into a list to reissue it later,
do it eagerly. It removes overhead on keeping and checking that list,
and allows in case of failure for these requests to be completed through
normal iopoll completion path.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1029,8 +1029,7 @@ static struct fixed_rsrc_ref_node *alloc_fixed_rsrc_ref_node(
 static void init_fixed_file_ref_node(struct io_ring_ctx *ctx,
 				     struct fixed_rsrc_ref_node *ref_node);
 
-static void __io_complete_rw(struct io_kiocb *req, long res, long res2,
-			     unsigned int issue_flags);
+static bool io_rw_reissue(struct io_kiocb *req, long res);
 static void io_cqring_fill_event(struct io_kiocb *req, long res);
 static void io_put_req(struct io_kiocb *req);
 static void io_put_req_deferred(struct io_kiocb *req, int nr);
@@ -2558,17 +2557,6 @@ static inline bool io_run_task_work(void)
 	return false;
 }
 
-static void io_iopoll_queue(struct list_head *again)
-{
-	struct io_kiocb *req;
-
-	do {
-		req = list_first_entry(again, struct io_kiocb, inflight_entry);
-		list_del(&req->inflight_entry);
-		__io_complete_rw(req, -EAGAIN, 0, 0);
-	} while (!list_empty(again));
-}
-
 /*
  * Find and free completed poll iocbs
  */
@@ -2577,7 +2565,6 @@ 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();
@@ -2587,13 +2574,13 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		int cflags = 0;
 
 		req = list_first_entry(done, struct io_kiocb, inflight_entry);
+		list_del(&req->inflight_entry);
+
 		if (READ_ONCE(req->result) == -EAGAIN) {
-			req->result = 0;
 			req->iopoll_completed = 0;
-			list_move_tail(&req->inflight_entry, &again);
+			if (io_rw_reissue(req, -EAGAIN))
 				continue;
 		}
-		list_del(&req->inflight_entry);
 
 		if (req->flags & REQ_F_BUFFER_SELECTED)
 			cflags = io_put_rw_kbuf(req);
@@ -2608,9 +2595,6 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 	io_commit_cqring(ctx);
 	io_cqring_ev_posted_iopoll(ctx);
 	io_req_free_batch_finish(ctx, &rb);
-
-	if (!list_empty(&again))
-		io_iopoll_queue(&again);
 }
 
 static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,