thread.c: reset waitq of keeping mutexes in child

We must not maintain references to threads in the parent process
in any mutexes held by the child process.

* thread_sync.c (rb_mutex_cleanup_keeping_mutexes): new function
* thread.c (rb_thread_atfork): cleanup keeping mutexes
  [ruby-core:85940] [Bug #14578]

Fixes: r58604 (commit 3586c9e0876e784767a1c1adba9ebc2499fa0ec2)
       ("reduce rb_mutex_t size from 160 to 80 bytes on 64-bit")

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62668 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 14 insertions, 0 deletions

diff --git a/thread_sync.c b/thread_sync.c
index e4a28ccb5c..8f68583a78 100644
--- a/thread_sync.c
+++ b/thread_sync.c
@@ -415,6 +415,20 @@ rb_mutex_abandon_all(rb_mutex_t *mutexes)
 	list_head_init(&mutex->waitq);
     }
 }
+
+/*
+ * All other threads are dead in the a new child process, so waitqs
+ * contain references to dead threads which we need to clean up
+ */
+static void
+rb_mutex_cleanup_keeping_mutexes(const rb_thread_t *current_thread)
+{
+    rb_mutex_t *mutex = current_thread->keeping_mutexes;
+    while (mutex) {
+        list_head_init(&mutex->waitq);
+        mutex = mutex->next_mutex;
+    }
+}
 #endif
 
 static VALUE