Lock pshared_lock shared around fork, to ensure that the COW snapshot

of the pshared hash in child is consistent and can be safely used.

Reported and tested by:	"Oleg V. Nauman" <oleg@opentransfer.com>
Sponsored by:	The FreeBSD Foundation

lib/libthr/thread/thr_fork.c

@@ -168,6 +168,7 @@ __thr_fork(void)
 	if (_thr_isthreaded() != 0) {
 		was_threaded = 1;
 		_malloc_prefork();
+		__thr_pshared_atfork_pre();
 		_rtld_atfork_pre(rtld_locks);
 	} else {
 		was_threaded = 0;
@@ -202,8 +203,10 @@ __thr_fork(void)
 
 		_thr_signal_postfork_child();
 
-		if (was_threaded)
+		if (was_threaded) {
 			_rtld_atfork_post(rtld_locks);
+			__thr_pshared_atfork_post();
+		}
 		_thr_setthreaded(0);
 
 		/* reinitalize library. */
@@ -236,6 +239,7 @@ __thr_fork(void)
 
 		if (was_threaded) {
 			_rtld_atfork_post(rtld_locks);
+			__thr_pshared_atfork_post();
 			_malloc_postfork();
 		}
 

lib/libthr/thread/thr_init.c

@@ -445,7 +445,6 @@ init_private(void)
 	_thr_once_init();
 	_thr_spinlock_init();
 	_thr_list_init();
-	__thr_pshared_init();
 	_thr_wake_addr_init();
 	_sleepq_init();
 	_single_thread = NULL;
@@ -456,6 +455,7 @@ init_private(void)
 	 * e.g. after a fork().
 	 */
 	if (init_once == 0) {
+		__thr_pshared_init();
 		/* Find the stack top */
 		mib[0] = CTL_KERN;
 		mib[1] = KERN_USRSTACK;

lib/libthr/thread/thr_private.h

@@ -952,6 +952,8 @@ void	_tcb_dtor(struct tcb *);
 void __thr_pshared_init(void) __hidden;
 void *__thr_pshared_offpage(void *key, int doalloc) __hidden;
 void __thr_pshared_destroy(void *key) __hidden;
+void __thr_pshared_atfork_pre(void) __hidden;
+void __thr_pshared_atfork_post(void) __hidden;
 
 __END_DECLS
 

lib/libthr/thread/thr_pshared.c

@@ -252,3 +252,17 @@ __thr_pshared_destroy(void *key)
 	pshared_clean(key, val);
 	pshared_gc(curthread);
 }
+
+void
+__thr_pshared_atfork_pre(void)
+{
+
+	_thr_rwl_rdlock(&pshared_lock);
+}
+
+void
+__thr_pshared_atfork_post(void)
+{
+
+	_thr_rwl_unlock(&pshared_lock);
+}