merge revision(s) 62934,63210,63215,63309: [Backport #14634]

	thread_sync.c: avoid reaching across stacks of dead threads

	rb_ensure is insufficient cleanup for fork and we must
	reinitialize all waitqueues in the child process.

	Unfortunately this increases the footprint of ConditionVariable,
	Queue and SizedQueue by 8 bytes on 32-bit (16 bytes on 64-bit).

	[ruby-core:86316] [Bug #14634]

	variable.c: fix thread + fork errors in autoload

	This is fairly non-intrusive bugfix to prevent children
	from trying to reach into thread stacks of the parent.
	I will probably reuse this idea and redo r62934, too
	(same bug).

	* vm_core.h (typedef struct rb_vm_struct): add fork_gen counter
	* thread.c (rb_thread_atfork_internal): increment fork_gen
	* variable.c (struct autoload_data_i): store fork_gen
	* variable.c (check_autoload_data): remove (replaced with get_...)
	* variable.c (get_autoload_data): check fork_gen when retrieving
	* variable.c (check_autoload_required): use get_autoload_data
	* variable.c (rb_autoloading_value): ditto
	* variable.c (rb_autoload_p): ditto
	* variable.c (current_autoload_data): ditto
	* variable.c (autoload_reset): reset fork_gen, adjust indent
	* variable.c (rb_autoload_load): set fork_gen when setting state
	* test/ruby/test_autoload.rb (test_autoload_fork): new test
	  [ruby-core:86410] [Bug #14634]

	thread_sync: redo r62934 to use fork_gen

	Instead of maintaining linked-lists to store all
	rb_queue/rb_szqueue/rb_condvar structs; store only a fork_gen
	serial number to simplify management of these items.

	This reduces initialization costs and avoids the up-front cost
	of resetting all Queue/SizedQueue/ConditionVariable objects at
	fork while saving 8 bytes per-structure on 64-bit.  There are no
	savings on 32-bit.

	* thread.c (rb_thread_atfork_internal): remove rb_thread_sync_reset_all call
	* thread_sync.c (rb_thread_sync_reset_all): remove
	* thread_sync.c (queue_live): remove
	* thread_sync.c (queue_free): remove
	* thread_sync.c (struct rb_queue): s/live/fork_gen/
	* thread_sync.c (queue_data_type): use default free
	* thread_sync.c (queue_alloc): remove list_add
	* thread_sync.c (queue_fork_check): new function
	* thread_sync.c (queue_ptr): call queue_fork_check
	* thread_sync.c (szqueue_free): remove
	* thread_sync.c (szqueue_data_type): use default free
	* thread_sync.c (szqueue_alloc): remove list_add
	* thread_sync.c (szqueue_ptr):  check fork_gen via queue_fork_check
	* thread_sync.c (struct rb_condvar): s/live/fork_gen/
	* thread_sync.c (condvar_free): remove
	* thread_sync.c (cv_data_type): use default free
	* thread_sync.c (condvar_ptr): check fork_gen
	* thread_sync.c (condvar_alloc): remove list_add
	  [ruby-core:86316] [Bug #14634]

	thread_sync.c (condvar_ptr): reset fork_gen after forking

	Otherwise the condition variable waiter list will always
	be empty, which is wrong :x

	[Bug #14725] [Bug #14634]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@66912 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 23 insertions, 9 deletions

diff --git a/variable.c b/variable.c
index f700303d2f..bfb6fa2edd 100644
--- a/variable.c
+++ b/variable.c
@@ -20,6 +20,7 @@
 #include "ccan/list/list.h"
 #include "id_table.h"
 #include "debug_counter.h"
+#include "vm_core.h"
 
 struct rb_id_table *rb_global_tbl;
 static ID autoload, classpath, tmp_classpath, classid;
@@ -1859,6 +1860,7 @@ struct autoload_data_i {
     rb_const_flag_t flag;
     VALUE value;
     struct autoload_state *state; /* points to on-stack struct */
+    rb_serial_t fork_gen;
 };
 
 static void
@@ -1881,8 +1883,18 @@ static const rb_data_type_t autoload_data_i_type = {
     0, 0, RUBY_TYPED_FREE_IMMEDIATELY
 };
 
-#define check_autoload_data(av) \
-    (struct autoload_data_i *)rb_check_typeddata((av), &autoload_data_i_type)
+static struct autoload_data_i *
+get_autoload_data(VALUE av)
+{
+    struct autoload_data_i *ele = rb_check_typeddata(av, &autoload_data_i_type);
+
+    /* do not reach across stack for ->state after forking: */
+    if (ele && ele->state && ele->fork_gen != GET_VM()->fork_gen) {
+        ele->state = 0;
+        ele->fork_gen = 0;
+    }
+    return ele;
+}
 
 RUBY_FUNC_EXPORTED void
 rb_autoload(VALUE mod, ID id, const char *file)
@@ -1982,7 +1994,7 @@ check_autoload_required(VALUE mod, ID id, const char **loadingpath)
     const char *loading;
     int safe;
 
-    if (!(load = autoload_data(mod, id)) || !(ele = check_autoload_data(load))) {
+    if (!(load = autoload_data(mod, id)) || !(ele = get_autoload_data(load))) {
 	return 0;
     }
     file = ele->feature;
@@ -2020,7 +2032,7 @@ rb_autoloading_value(VALUE mod, ID id, VALUE* value, rb_const_flag_t *flag)
     VALUE load;
     struct autoload_data_i *ele;
 
-    if (!(load = autoload_data(mod, id)) || !(ele = check_autoload_data(load))) {
+    if (!(load = autoload_data(mod, id)) || !(ele = get_autoload_data(load))) {
 	return 0;
     }
     if (ele->state && ele->state->thread == rb_thread_current()) {
@@ -2087,8 +2099,9 @@ autoload_reset(VALUE arg)
     int need_wakeups = 0;
 
     if (state->ele->state == state) {
-	need_wakeups = 1;
-	state->ele->state = 0;
+        need_wakeups = 1;
+        state->ele->state = 0;
+        state->ele->fork_gen = 0;
     }
 
     /* At the last, move a value defined in autoload to constant table */
@@ -2170,7 +2183,7 @@ rb_autoload_load(VALUE mod, ID id)
     if (src && loading && strcmp(src, loading) == 0) return Qfalse;
 
     /* set ele->state for a marker of autoloading thread */
-    if (!(ele = check_autoload_data(load))) {
+    if (!(ele = get_autoload_data(load))) {
 	return Qfalse;
     }
 
@@ -2180,6 +2193,7 @@ rb_autoload_load(VALUE mod, ID id)
     state.thread = rb_thread_current();
     if (!ele->state) {
 	ele->state = &state;
+	ele->fork_gen = GET_VM()->fork_gen;
 
 	/*
 	 * autoload_reset will wake up any threads added to this
@@ -2217,7 +2231,7 @@ rb_autoload_p(VALUE mod, ID id)
     }
     load = check_autoload_required(mod, id, 0);
     if (!load) return Qnil;
-    return (ele = check_autoload_data(load)) ? ele->feature : Qnil;
+    return (ele = get_autoload_data(load)) ? ele->feature : Qnil;
 }
 
 void
@@ -2646,7 +2660,7 @@ current_autoload_data(VALUE mod, ID id)
     struct autoload_data_i *ele;
     VALUE load = autoload_data(mod, id);
     if (!load) return 0;
-    ele = check_autoload_data(load);
+    ele = get_autoload_data(load);
     if (!ele) return 0;
     /* for autoloading thread, keep the defined value to autoloading storage */
     if (ele->state && (ele->state->thread == rb_thread_current())) {