io_uring: warn when ring exit takes too long

We use system_unbound_wq to run io_ring_exit_work(), so it's hard to
monitor whether removal hang or not. Add WARN_ONCE to catch hangs.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8560,6 +8560,7 @@ static void io_tctx_exit_cb(struct callback_head *cb)
 static void io_ring_exit_work(struct work_struct *work)
 {
 	struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx, exit_work);
+	unsigned long timeout = jiffies + HZ * 60 * 5;
 	struct io_tctx_exit exit;
 	struct io_tctx_node *node;
 	int ret;
@@ -8572,10 +8573,14 @@ static void io_ring_exit_work(struct work_struct *work)
 	 */
 	do {
 		io_uring_try_cancel_requests(ctx, NULL, NULL);
+
+		WARN_ON_ONCE(time_after(jiffies, timeout));
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 
 	mutex_lock(&ctx->uring_lock);
 	while (!list_empty(&ctx->tctx_list)) {
+		WARN_ON_ONCE(time_after(jiffies, timeout));
+
 		node = list_first_entry(&ctx->tctx_list, struct io_tctx_node,
 					ctx_node);
 		exit.ctx = ctx;