If a pane is killed, cancel reading from the file. GitHub issue 3422.

client.c

@@ -693,6 +693,9 @@ client_dispatch_wait(struct imsg *imsg)
 		    !(client_flags & CLIENT_CONTROL), client_file_check_cb,
 		    NULL);
 		break;
+	case MSG_READ_CANCEL:
+		file_read_cancel(&client_files, imsg);
+		break;
 	case MSG_WRITE_OPEN:
 		file_write_open(&client_files, client_peer, imsg, 1,
 		    !(client_flags & CLIENT_CONTROL), client_file_check_cb,

file.c

@@ -152,7 +152,8 @@ file_fire_done_cb(__unused int fd, __unused short events, void *arg)
 	struct client_file	*cf = arg;
 	struct client		*c = cf->c;
 
-	if (cf->cb != NULL && (c == NULL || (~c->flags & CLIENT_DEAD)))
+	if (cf->cb != NULL &&
+	    (cf->closed || c == NULL || (~c->flags & CLIENT_DEAD)))
 		cf->cb(c, cf->path, cf->error, 1, cf->buffer, cf->data);
 	file_free(cf);
 }
@@ -355,7 +356,7 @@ done:
 }
 
 /* Read a file. */
-void
+struct client_file *
 file_read(struct client *c, const char *path, client_file_cb cb, void *cbdata)
 {
 	struct client_file	*cf;
@@ -423,10 +424,27 @@ skip:
 		goto done;
 	}
 	free(msg);
-	return;
+	return cf;
 
 done:
 	file_fire_done(cf);
+	return NULL;
+}
+
+/* Cancel a file read. */
+void
+file_cancel(struct client_file *cf)
+{
+	struct msg_read_cancel	 msg;
+
+	log_debug("read cancel file %d", cf->stream);
+
+	if (cf->closed)
+		return;
+	cf->closed = 1;
+
+	msg.stream = cf->stream;
+	proc_send(cf->peer, MSG_READ_CANCEL, -1, &msg, sizeof msg);
 }
 
 /* Push event, fired if there is more writing to be done. */
@@ -760,6 +778,24 @@ reply:
 	proc_send(peer, MSG_READ_DONE, -1, &reply, sizeof reply);
 }
 
+/* Handle a read cancel message (client). */
+void
+file_read_cancel(struct client_files *files, struct imsg *imsg)
+{
+	struct msg_read_cancel	*msg = imsg->data;
+	size_t			 msglen = imsg->hdr.len - IMSG_HEADER_SIZE;
+	struct client_file	 find, *cf;
+
+	if (msglen != sizeof *msg)
+		fatalx("bad MSG_READ_CANCEL size");
+	find.stream = msg->stream;
+	if ((cf = RB_FIND(client_files, files, &find)) == NULL)
+		fatalx("unknown stream number");
+	log_debug("cancel file %d", cf->stream);
+
+	file_read_error_callback(NULL, 0, cf);
+}
+
 /* Handle a write ready message (server). */
 void
 file_write_ready(struct client_files *files, struct imsg *imsg)
@@ -797,7 +833,7 @@ file_read_data(struct client_files *files, struct imsg *imsg)
 		return;
 
 	log_debug("file %d read %zu bytes", cf->stream, bsize);
-	if (cf->error == 0) {
+	if (cf->error == 0 && !cf->closed) {
 		if (evbuffer_add(cf->buffer, bdata, bsize) != 0) {
 			cf->error = ENOMEM;
 			file_fire_done(cf);

tmux-protocol.h

@@ -66,7 +66,8 @@ enum msgtype {
 	MSG_WRITE_OPEN,
 	MSG_WRITE,
 	MSG_WRITE_READY,
-	MSG_WRITE_CLOSE
+	MSG_WRITE_CLOSE,
+	MSG_READ_CANCEL
 };
 
 /*
@@ -92,6 +93,10 @@ struct msg_read_done {
 	int	error;
 };
 
+struct msg_read_cancel {
+	int	stream;
+};
+
 struct msg_write_open {
 	int	stream;
 	int	fd;

tmux.h

@@ -2611,7 +2611,9 @@ void	 file_print_buffer(struct client *, void *, size_t);
 void printflike(2, 3) file_error(struct client *, const char *, ...);
 void	 file_write(struct client *, const char *, int, const void *, size_t,
 	     client_file_cb, void *);
-void	 file_read(struct client *, const char *, client_file_cb, void *);
+struct client_file *file_read(struct client *, const char *, client_file_cb,
+	     void *);
+void	 file_cancel(struct client_file *);
 void	 file_push(struct client_file *);
 int	 file_write_left(struct client_files *);
 void	 file_write_open(struct client_files *, struct tmuxpeer *,
@@ -2623,6 +2625,7 @@ void	 file_read_open(struct client_files *, struct tmuxpeer *, struct imsg *,
 void	 file_write_ready(struct client_files *, struct imsg *);
 void	 file_read_data(struct client_files *, struct imsg *);
 void	 file_read_done(struct client_files *, struct imsg *);
+void	 file_read_cancel(struct client_files *, struct imsg *);
 
 /* server.c */
 extern struct tmuxproc *server_proc;

window.c

@@ -66,6 +66,7 @@ static u_int	next_active_point;
 struct window_pane_input_data {
 	struct cmdq_item	*item;
 	u_int			 wp;
+	struct client_file	*file;
 };
 
 static struct window_pane *window_pane_create(struct window *, u_int, u_int,
@@ -1533,18 +1534,16 @@ window_pane_input_callback(struct client *c, __unused const char *path,
 	size_t				 len = EVBUFFER_LENGTH(buffer);
 
 	wp = window_pane_find_by_id(cdata->wp);
-	if (wp == NULL || closed || error != 0 || (c->flags & CLIENT_DEAD)) {
+	if (cdata->file != NULL && (wp == NULL || c->flags & CLIENT_DEAD)) {
 		if (wp == NULL)
 			c->flags |= CLIENT_EXIT;
-
-		evbuffer_drain(buffer, len);
+		file_cancel(cdata->file);
+	} else if (cdata->file == NULL || closed || error != 0) {
 		cmdq_continue(cdata->item);
-
 		server_client_unref(c);
 		free(cdata);
-		return;
-	}
-	input_parse_buffer(wp, buf, len);
+	} else
+		input_parse_buffer(wp, buf, len);
 	evbuffer_drain(buffer, len);
 }
 
@@ -1567,9 +1566,8 @@ window_pane_start_input(struct window_pane *wp, struct cmdq_item *item,
 	cdata = xmalloc(sizeof *cdata);
 	cdata->item = item;
 	cdata->wp = wp->id;
-
+	cdata->file = file_read(c, "-", window_pane_input_callback, cdata);
 	c->references++;
-	file_read(c, "-", window_pane_input_callback, cdata);
 
 	return (0);
 }