utrace-resume-fix.patch

commit 2a73da6fc0913bc08fb249138937765fceb7e650
Author: Sultan Alsawaf <sultan@openresty.com>
Date:   Wed Sep 30 21:09:31 2020 -0700

    task_finder2: don't filter out UTRACE_RESUME actions to fix stapio Dl+ hangs
    
    UTRACE_RESUME is the complement to UTRACE_STOP, and currently it is always
    ignored. So when UTRACE_STOP is done, the traced process can remain stuck
    sleeping forever inside the utrace_stop() function at the schedule() line.
    The only ways to wake the sleeping process from its endless sleep are to
    either send a SIGKILL to it or to restore it with UTRACE_RESUME.
    
    When processes hang due to this bug, stp_task_work_exit() loops forever
    waiting for the stp_task_work_callbacks counter to hit zero, which will
    never happen.

diff --git a/runtime/linux/task_finder2.c b/runtime/linux/task_finder2.c
index 0ba614741..917ec46f1 100644
--- a/runtime/linux/task_finder2.c
+++ b/runtime/linux/task_finder2.c
@@ -553,20 +553,18 @@ __stp_utrace_attach(struct task_struct *tsk,
 		if (rc == 0) {
 			debug_task_finder_attach();
 
-			if (action != UTRACE_RESUME) {
-				rc = utrace_control(tsk, engine, action);
-				dbug_task(2, "utrace_control(%d) returned %d", action, rc);
-				/* If utrace_control() returns
-				 * EINPROGRESS when we're trying to
-				 * stop/interrupt, that means the task
-				 * hasn't stopped quite yet, but will
-				 * soon.  Ignore this error. */
-				if (rc != 0 && rc != -EINPROGRESS) {
-					_stp_error("utrace_control returned error %d on pid %d",
-						   rc, (int)tsk->pid);
-				}
-				rc = 0;
+			rc = utrace_control(tsk, engine, action);
+			dbug_task(2, "utrace_control(%d) returned %d", action, rc);
+			/* If utrace_control() returns
+			 * EINPROGRESS when we're trying to
+			 * stop/interrupt, that means the task
+			 * hasn't stopped quite yet, but will
+			 * soon.  Ignore this error. */
+			if (rc != 0 && rc != -EINPROGRESS) {
+				_stp_error("utrace_control returned error %d on pid %d",
+					   rc, (int)tsk->pid);
 			}
+			rc = 0;
 		}
 		else if (rc != -ESRCH && rc != -EALREADY)
 			_stp_error("utrace_set_events2 returned error %d on pid %d",