Re: Memory coherency issue with IO thread offloading?

@@ -850,6 +865,8 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags)
 	return kiocb_done(req, ret, issue_flags);
 }
 
+static int io_rewrite_queue(struct io_kiocb *req);
+
 int io_write(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);

@@ -974,7 +991,9 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 		if (!ret) {
 			if (kiocb->ki_flags & IOCB_WRITE)
 				kiocb_end_write(req);
-			return -EAGAIN;
+			if (io_rewrite_queue(req))
+				return -EAGAIN;
+			return IOU_ISSUE_SKIP_COMPLETE;
 		}
 		return ret;
 	}

@@ -984,6 +1003,45 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	return ret;
 }
 
+struct koffload {
+	struct work_struct work;
+	struct io_kiocb *req;
+	struct mm_struct *mm;
+};
+
+static void io_rewrite(struct work_struct *work)
+{
+	struct koffload *k = container_of(work, struct koffload, work);
+	unsigned issue_flags = IO_URING_F_UNLOCKED;
+	int ret;
+
+	kthread_use_mm(k->mm);
+	ret = io_write(k->req, issue_flags);
+	kthread_unuse_mm(k->mm);
+	mmput(k->mm);
+
+	if (ret != IOU_ISSUE_SKIP_COMPLETE)
+		io_req_complete_post(k->req, issue_flags);
+	kfree(k);
+}
+
+static int io_rewrite_queue(struct io_kiocb *req)
+{
+	struct koffload *k;
+
+	k = kmalloc(sizeof(*k), GFP_NOIO);
+	if (!k)
+		return 1;
+
+	INIT_WORK(&k->work, io_rewrite);
+	k->req = req;
+	mmget(current->mm);
+	k->mm = current->mm;
+	queue_work(system_wq, &k->work);
+	return 0;
+}
+
+
 static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
 {
 	io_commit_cqring_flush(ctx);