io_uring: break out of iowq iopoll on teardown

[ upstream commit 45500dc ]

io-wq will retry iopoll even when it failed with -EAGAIN. If that
races with task exit, which sets TIF_NOTIFY_SIGNAL for all its workers,
such workers might potentially infinitely spin retrying iopoll again and
again and each time failing on some allocation / waiting / etc. Don't
keep spinning if io-wq is dying.

Fixes: 561fb04 ("io_uring: replace workqueue usage with io-wq")
Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

io_uring/io-wq.c

@@ -181,6 +181,16 @@ static void io_worker_ref_put(struct io_wq *wq)
 		complete(&wq->worker_done);
 }
 
+bool io_wq_worker_stopped(void)
+{
+	struct io_worker *worker = current->worker_private;
+
+	if (WARN_ON_ONCE(!io_wq_current_is_worker()))
+		return true;
+
+	return test_bit(IO_WQ_BIT_EXIT, &worker->wqe->wq->state);
+}
+
 static void io_worker_cancel_cb(struct io_worker *worker)
 {
 	struct io_wqe_acct *acct = io_wqe_get_acct(worker);

io_uring/io-wq.h

@@ -52,6 +52,7 @@ void io_wq_hash_work(struct io_wq_work *work, void *val);
 
 int io_wq_cpu_affinity(struct io_wq *wq, cpumask_var_t mask);
 int io_wq_max_workers(struct io_wq *wq, int *new_count);
+bool io_wq_worker_stopped(void);
 
 static inline bool io_wq_is_hashed(struct io_wq_work *work)
 {

io_uring/io_uring.c

@@ -1823,6 +1823,8 @@ void io_wq_submit_work(struct io_wq_work *work)
 		if (!needs_poll) {
 			if (!(req->ctx->flags & IORING_SETUP_IOPOLL))
 				break;
+			if (io_wq_worker_stopped())
+				break;
 			cond_resched();
 			continue;
 		}