[LEDE-DEV] ubus/libubox: SIGTERM/SIGINT signals received during ubus_complete_request() calls are ignored

[Felix Fietkau]

Hi Alin,

On 2017-02-03 09:29, Alin Năstac wrote:
> Hi Felix,
> 
> SIGTERM & SIGINT signals received during ubus_complete_request()
> waiting for ubus_poll_data() to return are ignored due to
> uloop_cancelled being restored to its previous value it had before
> uloop_poll_data() was called.
> 
> The reproduction scenario is this:
>   1) cancelled local variable is set to false, current value of uloop_cancelled
>   2) while ubus_poll_data() is waiting for a read event, a SIGTERM is
> received, so uloop_cancelled is set to true
>   3) after ubus_poll_data() returns, uloop_cancelled value gets
> overwritten with false and SIGTERM signal ends up being ignored in the
> uloop_run()
> 
> The whole uloop_cancelled related logic in the ubus_complete_request()
> seems to be focused on getting out from the current recursion of
> uloop_run(), but from what I see uloop_run() capability to be called
> recursively is no longer used in ubus, so I wonder if it is still
> necessary.
I left in uloop_cancelled primarily to deal with cleaning up recursive
requests after Ctrl+c or SIGTERM when uloop is in use.

> If the answer is no, the entire logic referring to uloop_cancelled and
> uloop_end() should be removed from libubus-req.c. Otherwise an
> additional uloop_cancelled_recursions bit mask would be needed that
> will allow to control uloop_run() exit condition for each individual
> recursion.
I think the main problem was the fact that uloop_cancelled was used
both for internal request termination and also for external use.
Here's a patch that should resolve this issue, please test:

---
diff --git a/libubus-io.c b/libubus-io.c
index 1075c65..1343bb2 100644
--- a/libubus-io.c
+++ b/libubus-io.c
@@ -154,9 +154,10 @@ int __hidden ubus_send_msg(struct ubus_context *ctx, uint32_t seq,
 	return ret;
 }
 
-static int recv_retry(int fd, struct iovec *iov, bool wait, int *recv_fd)
+static int recv_retry(struct ubus_context *ctx, struct iovec *iov, bool wait, int *recv_fd)
 {
 	int bytes, total = 0;
+	int fd = ctx->sock.fd;
 	static struct {
 		struct cmsghdr h;
 		int fd;
@@ -191,7 +192,7 @@ static int recv_retry(int fd, struct iovec *iov, bool wait, int *recv_fd)
 
 		if (bytes < 0) {
 			bytes = 0;
-			if (uloop_cancelled)
+			if (uloop_cancelled || ctx->cancel_poll)
 				return 0;
 			if (errno == EINTR)
 				continue;
@@ -274,7 +275,7 @@ static bool get_next_msg(struct ubus_context *ctx, int *recv_fd)
 	int r;
 
 	/* receive header + start attribute */
-	r = recv_retry(ctx->sock.fd, &iov, false, recv_fd);
+	r = recv_retry(ctx, &iov, false, recv_fd);
 	if (r <= 0) {
 		if (r < 0)
 			ctx->sock.eof = true;
@@ -298,7 +299,7 @@ static bool get_next_msg(struct ubus_context *ctx, int *recv_fd)
 	iov.iov_base = (char *)ctx->msgbuf.data + sizeof(hdrbuf.data);
 	iov.iov_len = blob_len(ctx->msgbuf.data);
 	if (iov.iov_len > 0 &&
-	    recv_retry(ctx->sock.fd, &iov, true, NULL) <= 0)
+	    recv_retry(ctx, &iov, true, NULL) <= 0)
 		return false;
 
 	return true;
@@ -311,7 +312,7 @@ void __hidden ubus_handle_data(struct uloop_fd *u, unsigned int events)
 
 	while (get_next_msg(ctx, &recv_fd)) {
 		ubus_process_msg(ctx, &ctx->msgbuf, recv_fd);
-		if (uloop_cancelled)
+		if (uloop_cancelled || ctx->cancel_poll)
 			break;
 	}
 
@@ -326,6 +327,7 @@ void __hidden ubus_poll_data(struct ubus_context *ctx, int timeout)
 		.events = POLLIN | POLLERR,
 	};
 
+	ctx->cancel_poll = false;
 	poll(&pfd, 1, timeout ? timeout : -1);
 	ubus_handle_data(&ctx->sock, ULOOP_READ);
 }
diff --git a/libubus-req.c b/libubus-req.c
index db5061c..305e813 100644
--- a/libubus-req.c
+++ b/libubus-req.c
@@ -122,7 +122,7 @@ static void ubus_sync_req_cb(struct ubus_request *req, int ret)
 {
 	req->status_msg = true;
 	req->status_code = ret;
-	uloop_end();
+	req->ctx->cancel_poll = true;
 }
 
 static int64_t get_time_msec(void)
@@ -142,6 +142,7 @@ int ubus_complete_request(struct ubus_context *ctx, struct ubus_request *req,
 	ubus_complete_handler_t complete_cb = req->complete_cb;
 	int status = UBUS_STATUS_NO_DATA;
 	int64_t timeout = 0, time_end = 0;
+	bool prev_uloop_cancelled = uloop_cancelled;
 
 	if (req_timeout)
 		time_end = get_time_msec() + req_timeout;
@@ -149,29 +150,32 @@ int ubus_complete_request(struct ubus_context *ctx, struct ubus_request *req,
 	ubus_complete_request_async(ctx, req);
 	req->complete_cb = ubus_sync_req_cb;
 
+	if (!ctx->stack_depth)
+		uloop_cancelled = false;
+
 	ctx->stack_depth++;
 	while (!req->status_msg) {
-		bool cancelled = uloop_cancelled;
-
-		uloop_cancelled = false;
 		if (req_timeout) {
 			timeout = time_end - get_time_msec();
 			if (timeout <= 0) {
 				ubus_set_req_status(req, UBUS_STATUS_TIMEOUT);
-				uloop_cancelled = cancelled;
 				break;
 			}
 		}
+
 		ubus_poll_data(ctx, (unsigned int) timeout);
 
-		uloop_cancelled = cancelled;
 		if (ctx->sock.eof) {
 			ubus_set_req_status(req, UBUS_STATUS_CONNECTION_FAILED);
+			ctx->cancel_poll = true;
 			break;
 		}
 	}
+
 	ctx->stack_depth--;
 	if (ctx->stack_depth)
+		ctx->cancel_poll = true;
+	else if (prev_uloop_cancelled)
 		uloop_cancelled = true;
 
 	if (req->status_msg)
diff --git a/libubus.h b/libubus.h
index ea53272..4e45cb6 100644
--- a/libubus.h
+++ b/libubus.h
@@ -155,6 +155,7 @@ struct ubus_context {
 
 	uint32_t local_id;
 	uint16_t request_seq;
+	bool cancel_poll;
 	int stack_depth;
 
 	void (*connection_lost)(struct ubus_context *ctx);