parasite: stop a parasite daemon before dumping threads

The parasite daemon set up SIGCHLD handler, but for dumping threads we
use parasite-trap. While doing this the sigchild handler notices the
CHLD arriving on the thread trap, emits an error

(00.020292) Error (parasite-syscall.c:387): si_code=4 si_pid=3485 si_status=5

but wait() reports -1 (task is not dead, just trapped) and handler just exits.

Let's stop a parasite daemon before dumping threads.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -1626,15 +1626,21 @@ static int dump_one_task(struct pstree_item *item)
 		goto err_cure;
 	}
 
-	ret = dump_task_threads(parasite_ctl, item);
+	ret = dump_task_creds(parasite_ctl, cr_imgset, &cr);
 	if (ret) {
-		pr_err("Can't dump threads\n");
-		goto err_cure;
+		pr_err("Dump creds (pid: %d) failed with %d\n", pid, ret);
+		goto err;
 	}
 
-	ret = dump_task_creds(parasite_ctl, cr_imgset, &cr);
+	ret = parasite_stop_daemon(parasite_ctl);
 	if (ret) {
-		pr_err("Dump creds (pid: %d) failed with %d\n", pid, ret);
+		pr_err("Can't cure (pid: %d) from parasite\n", pid);
+		goto err;
+	}
+
+	ret = dump_task_threads(parasite_ctl, item);
+	if (ret) {
+		pr_err("Can't dump threads\n");
 		goto err;
 	}
 

include/parasite-syscall.h

@@ -136,6 +136,7 @@ enum trace_flags {
 	TRACE_EXIT,
 };
 
+extern int parasite_stop_daemon(struct parasite_ctl *ctl);
 extern int parasite_stop_on_syscall(int tasks, int sys_nr, enum trace_flags trace);
 extern int parasite_unmap(struct parasite_ctl *ctl, unsigned long addr);
 extern int ptrace_stop_pie(pid_t pid, void *addr, enum trace_flags *tf);

parasite-syscall.c

@@ -831,9 +831,6 @@ static int parasite_fini_seized(struct parasite_ctl *ctl)
 	if (restore_child_handler())
 		return -1;
 
-	if (!ctl->daemonized)
-		return 0;
-
 	/* Start to trace syscalls for each thread */
 	if (ptrace(PTRACE_INTERRUPT, pid, NULL, NULL)) {
 		pr_perror("Unable to interrupt the process");
@@ -970,15 +967,33 @@ goon:
 	return 0;
 }
 
-int parasite_cure_remote(struct parasite_ctl *ctl)
+int parasite_stop_daemon(struct parasite_ctl *ctl)
 {
-	int ret = 0;
+	if (ctl->daemonized) {
+		/*
+		 * Looks like a previous attempt failed, we should do
+		 * nothing in this case. parasite will try to cure itself.
+		 */
+		if (ctl->tsock < 0)
+			return -1;
 
-	if (ctl->parasite_ip)
-		if (parasite_fini_seized(ctl))
+		if (parasite_fini_seized(ctl)) {
+			close_safe(&ctl->tsock);
 			return -1;
+		}
+	}
 
-	close_safe(&ctl->tsock);
+	ctl->daemonized = false;
+
+	return 0;
+}
+
+int parasite_cure_remote(struct parasite_ctl *ctl)
+{
+	int ret = 0;
+
+	if (parasite_stop_daemon(ctl))
+		return -1;
 
 	if (ctl->remote_map) {
 		struct parasite_unmap_args *args;