io_uring: ensure finish_wait() is always called in __io_uring_task_cancel()

If we enter with requests pending and performm cancelations, we'll have
a different inflight count before and after calling prepare_to_wait().
This causes the loop to restart. If we actually ended up canceling
everything, or everything completed in-between, then we'll break out
of the loop without calling finish_wait() on the waitqueue. This can
trigger a warning on exit_signals(), as we leave the task state in
TASK_UNINTERRUPTIBLE.

Put a finish_wait() after the loop to catch that case.

Cc: stable@vger.kernel.org # 5.9+
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -9101,6 +9101,7 @@ void __io_uring_task_cancel(void)
 		finish_wait(&tctx->wait, &wait);
 	} while (1);
 
+	finish_wait(&tctx->wait, &wait);
 	atomic_dec(&tctx->in_idle);
 
 	io_uring_remove_task_files(tctx);