io_uring: wake SQPOLL task when task_work is added to an empty queue

If there's no current work on the list, we still need to potentially
wake the SQPOLL task if it is sleeping. This is ordered with the
wait queue addition in sqpoll, which adds to the wait queue before
checking for pending work items.

Fixes: af5d68f ("io_uring/sqpoll: manage task_work privately")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/io_uring.c

@@ -1370,8 +1370,13 @@ static void io_req_normal_work_add(struct io_kiocb *req)
 		atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
 
 	/* SQPOLL doesn't need the task_work added, it'll run it itself */
-	if (ctx->flags & IORING_SETUP_SQPOLL)
+	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		struct io_sq_data *sqd = ctx->sq_data;
+
+		if (wq_has_sleeper(&sqd->wait))
+			wake_up(&sqd->wait);
 		return;
+	}
 
 	if (likely(!task_work_add(req->task, &tctx->task_work, ctx->notify_method)))
 		return;