[PATCH 4/4] io_uring: re-issue plug based block requests that failed

[Jens Axboe <axboe@kernel.dk>]

Mark the plug with nowait == true, which will cause requests to avoid
blocking on request allocation. If they do, we catch them and add them
to the plug list. Once we finish the plug, re-issue requests that got
caught.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 625578715d37..04b3571b21e9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1947,12 +1947,31 @@ static void io_complete_rw_common(struct kiocb *kiocb, long res)
 	__io_cqring_add_event(req, res, cflags);
 }
 
+static bool io_rw_reissue(struct io_kiocb *req, long res)
+{
+#ifdef CONFIG_BLOCK
+	struct blk_plug *plug;
+
+	if ((res != -EAGAIN && res != -EOPNOTSUPP) || io_wq_current_is_worker())
+		return false;
+
+	plug = current->plug;
+	if (plug && plug->nowait) {
+		list_add_tail(&req->list, &plug->nowait_list);
+		return true;
+	}
+#endif
+	return false;
+}
+
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw.kiocb);
 
-	io_complete_rw_common(kiocb, res);
-	io_put_req(req);
+	if (!io_rw_reissue(req, res)) {
+		io_complete_rw_common(kiocb, res);
+		io_put_req(req);
+	}
 }
 
 static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
@@ -5789,12 +5808,30 @@ static int io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	return 0;
 }
 
+#ifdef CONFIG_BLOCK
+static void io_resubmit_rw(struct list_head *list)
+{
+	struct io_kiocb *req;
+
+	while (!list_empty(list)) {
+		req = list_first_entry(list, struct io_kiocb, list);
+		list_del(&req->list);
+		refcount_inc(&req->refs);
+		io_queue_async_work(req);
+	}
+}
+#endif
+
 /*
  * Batched submission is done, ensure local IO is flushed out.
  */
 static void io_submit_state_end(struct io_submit_state *state)
 {
 	blk_finish_plug(&state->plug);
+#ifdef CONFIG_BLOCK
+	if (unlikely(!list_empty(&state->plug.nowait_list)))
+		io_resubmit_rw(&state->plug.nowait_list);
+#endif
 	io_state_file_put(state);
 	if (state->free_reqs)
 		kmem_cache_free_bulk(req_cachep, state->free_reqs, state->reqs);
@@ -5807,6 +5844,10 @@ static void io_submit_state_start(struct io_submit_state *state,
 				  unsigned int max_ios)
 {
 	blk_start_plug(&state->plug);
+#ifdef CONFIG_BLOCK
+	INIT_LIST_HEAD(&state->plug.nowait_list);
+	state->plug.nowait = true;
+#endif
 	state->free_reqs = 0;
 	state->file = NULL;
 	state->ios_left = max_ios;
-- 
2.27.0