io_uring/msg_ring: reuse ctx->submitter_task read using READ_ONCE instead of re-reading it

In io_msg_exec_remote(), ctx->submitter_task is read using READ_ONCE at
the beginning of the function, checked, and then re-read from
ctx->submitter_task, voiding all guarantees of the checks. Reuse the value
that was read by READ_ONCE to ensure the consistency of the task struct
throughout the function.
Signed-off-by: linke li <lilinke99@qq.com>
Link: https://lore.kernel.org/r/tencent_F9B2296C93928D6F68FF0C95C33475C68209@qq.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/msg_ring.c

@@ -83,7 +83,7 @@ static int io_msg_exec_remote(struct io_kiocb *req, task_work_func_t func)
 		return -EOWNERDEAD;
 
 	init_task_work(&msg->tw, func);
-	if (task_work_add(ctx->submitter_task, &msg->tw, TWA_SIGNAL))
+	if (task_work_add(task, &msg->tw, TWA_SIGNAL))
 		return -EOWNERDEAD;
 
 	return IOU_ISSUE_SKIP_COMPLETE;