io_uring: hold uring_lock while completing failed polled io in io_wq_submit_work()

io_iopoll_complete() does not hold completion_lock to complete polled io,
so in io_wq_submit_work(), we can not call io_req_complete() directly, to
complete polled io, otherwise there maybe concurrent access to cqring,
defer_list, etc, which is not safe. Commit dad1b124 ("io_uring: always
let io_iopoll_complete() complete polled io") has fixed this issue, but
Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is not
good.

Given that io_iopoll_complete() is always called under uring_lock, so here
for polled io, we can also get uring_lock to fix this issue.

Fixes: dad1b124 ("io_uring: always let io_iopoll_complete() complete polled io")
Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
[axboe: don't deref 'req' after completing it']
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -6332,19 +6332,28 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
 	}
 
 	if (ret) {
+		struct io_ring_ctx *lock_ctx = NULL;
+
+		if (req->ctx->flags & IORING_SETUP_IOPOLL)
+			lock_ctx = req->ctx;
+
 		/*
-		 * io_iopoll_complete() does not hold completion_lock to complete
-		 * polled io, so here for polled io, just mark it done and still let
-		 * io_iopoll_complete() complete it.
+		 * io_iopoll_complete() does not hold completion_lock to
+		 * complete polled io, so here for polled io, we can not call
+		 * io_req_complete() directly, otherwise there maybe concurrent
+		 * access to cqring, defer_list, etc, which is not safe. Given
+		 * that io_iopoll_complete() is always called under uring_lock,
+		 * so here for polled io, we also get uring_lock to complete
+		 * it.
 		 */
-		if (req->ctx->flags & IORING_SETUP_IOPOLL) {
-			struct kiocb *kiocb = &req->rw.kiocb;
+		if (lock_ctx)
+			mutex_lock(&lock_ctx->uring_lock);
 
-			kiocb_done(kiocb, ret, NULL);
-		} else {
 		req_set_fail_links(req);
 		io_req_complete(req, ret);
-		}
+
+		if (lock_ctx)
+			mutex_unlock(&lock_ctx->uring_lock);
 	}
 
 	return io_steal_work(req);