[src/trunk]: src/lib/libpthread pthread_exit(): it looks there there is at le...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7209838aa204
branches:  trunk
changeset: 1006731:7209838aa204
user:      ad <ad%NetBSD.org@localhost>
date:      Sat Jan 25 18:01:28 2020 +0000

description:
pthread_exit(): it looks there there is at least one path through which
a thread can exit with waiters still hanging off it (cancellation when
waiting on a condvar) so deal with all/any crappy failure like that and
make sure there are never any waiters left before exiting.  Maybe of help
for:

PR: bin/50350: rump/rumpkern/t_sp/stress_{long,short} fail on Core 2

diffstat:

 lib/libpthread/pthread.c |  28 +++++++++++++++++++++++++---
 1 files changed, 25 insertions(+), 3 deletions(-)

diffs (68 lines):

diff -r 07a43cd4addb -r 7209838aa204 lib/libpthread/pthread.c
--- a/lib/libpthread/pthread.c  Sat Jan 25 17:58:28 2020 +0000
+++ b/lib/libpthread/pthread.c  Sat Jan 25 18:01:28 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pthread.c,v 1.155 2020/01/25 15:41:52 ad Exp $ */
+/*     $NetBSD: pthread.c,v 1.156 2020/01/25 18:01:28 ad Exp $ */
 
 /*-
  * Copyright (c) 2001, 2002, 2003, 2006, 2007, 2008, 2020
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__RCSID("$NetBSD: pthread.c,v 1.155 2020/01/25 15:41:52 ad Exp $");
+__RCSID("$NetBSD: pthread.c,v 1.156 2020/01/25 18:01:28 ad Exp $");
 
 #define        __EXPOSE_STACK  1
 
@@ -621,6 +621,23 @@
        return errno;
 }
 
+/*
+ * In case the thread is exiting at an inopportune time leaving waiters not
+ * awoken (because cancelled, for instance) make sure we have no waiters
+ * left.
+ */
+static void
+pthread__clear_waiters(pthread_t self)
+{
+
+       if (self->pt_nwaiters != 0) {
+               (void)_lwp_unpark_all(self->pt_waiters, self->pt_nwaiters,
+                   NULL);
+               self->pt_nwaiters = 0;
+       }
+       self->pt_willpark = 0;
+}
+
 void
 pthread_exit(void *retval)
 {
@@ -658,7 +675,10 @@
        /* Perform cleanup of thread-specific data */
        pthread__destroy_tsd(self);
 
-       /* Signal our exit. */
+       /*
+        * Signal our exit.  Our stack and pthread_t won't be reused until
+        * pthread_create() can see from kernel info that this LWP is gone.
+        */
        self->pt_exitval = retval;
        if (self->pt_flags & PT_FLAG_DETACHED) {
                self->pt_state = PT_STATE_DEAD;
@@ -670,11 +690,13 @@
                pthread_mutex_lock(&pthread__deadqueue_lock);
                PTQ_INSERT_TAIL(&pthread__deadqueue, self, pt_deadq);
                pthread_mutex_unlock(&pthread__deadqueue_lock);
+               pthread__clear_waiters(self);
                _lwp_exit();
        } else {
                self->pt_state = PT_STATE_ZOMBIE;
                pthread_cond_broadcast(&self->pt_joiners);
                pthread_mutex_unlock(&self->pt_lock);
+               pthread__clear_waiters(self);
                /* Note: name will be freed by the joiner. */
                _lwp_exit();
        }