thread_sync.c (mutex_ptr): handle mutexes held by parent threads in children

Mutexes may be held by threads which only exist in the parent
process, so their waitqueues may be populated with references
to other dead threads.  We must reset them at fork.

I am a moron for introducing this bug :<

[ruby-core:90312] [Bug #15383]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66230 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 11 insertions, 0 deletions

diff --git a/thread_sync.c b/thread_sync.c
index b79db1fee3..e478a96b88 100644
--- a/thread_sync.c
+++ b/thread_sync.c
@@ -45,6 +45,7 @@ typedef struct rb_mutex_struct {
     rb_thread_t *th;
     struct rb_mutex_struct *next_mutex;
     struct list_head waitq; /* protected by GVL */
+    rb_serial_t fork_gen;
 } rb_mutex_t;
 
 #if defined(HAVE_WORKING_FORK)
@@ -121,8 +122,18 @@ static rb_mutex_t *
 mutex_ptr(VALUE obj)
 {
     rb_mutex_t *mutex;
+    rb_serial_t fork_gen = GET_VM()->fork_gen;
 
     TypedData_Get_Struct(obj, rb_mutex_t, &mutex_data_type, mutex);
+
+    if (mutex->fork_gen != fork_gen) {
+        /* forked children can't reach into parent thread stacks */
+        mutex->fork_gen = fork_gen;
+        list_head_init(&mutex->waitq);
+        mutex->next_mutex = 0;
+        mutex->th = 0;
+    }
+
     return mutex;
 }