io_uring: use right task for exiting checks

When we use delayed_work for fallback execution of requests, current
will be not of the submitter task, and so checks in io_req_task_submit()
may not behave as expected. Currently, it leaves inline completions not
flushed, so making io_ring_exit_work() to hang. Use the submitter task
for all those checks.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/cb413c715bed0bc9c98b169059ea9c8a2c770715.1625881431.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2016,7 +2016,7 @@ static void io_req_task_submit(struct io_kiocb *req)
 
 	/* ctx stays valid until unlock, even if we drop all ours ctx->refs */
 	mutex_lock(&ctx->uring_lock);
-	if (!(current->flags & PF_EXITING) && !current->in_execve)
+	if (!(req->task->flags & PF_EXITING) && !req->task->in_execve)
 		__io_queue_sqe(req);
 	else
 		io_req_complete_failed(req, -EFAULT);