i#2157 re-attach: Add timeout to os_thread_suspend

After 5 seconds of waiting for a thread to acknowledge a received
signal, os_thread_suspend now returns false so that the caller can
retry.

Issue #2157

core/synch.c

@@ -1922,10 +1922,10 @@ detach_on_permanent_stack(bool internal, bool do_cleanup)
     DEBUG_DECLARE(bool ok;)
     DEBUG_DECLARE(int exit_res;)
     /* synch-all flags: if we fail to suspend a thread (e.g., privilege
-     * problems) ignore it.  XXX Should we retry instead?
+     * problems) retry it.
      */
     /* i#297: we only synch client threads after process exit event. */
-    uint flags = THREAD_SYNCH_SUSPEND_FAILURE_IGNORE | THREAD_SYNCH_SKIP_CLIENT_THREAD;
+    uint flags = THREAD_SYNCH_SUSPEND_FAILURE_RETRY | THREAD_SYNCH_SKIP_CLIENT_THREAD;
 
     ENTERING_DR();
 

core/unix/os.c

@@ -3474,10 +3474,17 @@ os_thread_suspend(thread_record_t *tr)
      */
     mutex_unlock(&ostd->suspend_lock);
     while (ksynch_get_value(&ostd->suspended) == 0) {
-        /* For Linux, waits only if the suspended flag is not set as 1. Return value
-         * doesn't matter because the flag will be re-checked.
+        /* For Linux, waits only if the suspended flag is not set as 1. Other
+         * than a timeout value, the return value doesn't matter because the
+         * flag will be re-checked.
          */
-        ksynch_wait(&ostd->suspended, 0, 0);
+        if (ksynch_wait(&ostd->suspended, 0, 5000) == -ETIMEDOUT) {
+            mutex_lock(&ostd->suspend_lock);
+            ASSERT(ostd->suspend_count > 0);
+            ostd->suspend_count--;
+            mutex_unlock(&ostd->suspend_lock);
+            return false;
+        }
         if (ksynch_get_value(&ostd->suspended) == 0) {
             /* If it still has to wait, give up the cpu. */
             os_thread_yield();