From ac543abe91d7325ace7254f635f34e71e1faaf2e Mon Sep 17 00:00:00 2001
From: normal <normal@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Wed, 29 Aug 2018 08:04:09 +0000
Subject: [PATCH] cont.c: set th->root_fiber to current fiber at fork

Otherwise, th->root_fiber can point to an invalid Fiber,
because Fibers do not live across fork.  So consider
whatever Fiber is running the root fiber.

[ruby-core:88723] [Bug #15041]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64589 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 cont.c                  | 12 ++++++++++++
 test/ruby/test_fiber.rb |  6 +++++-
 thread.c                |  2 ++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/cont.c b/cont.c
index c400640dc4..3f0a5cb45f 100644
--- a/cont.c
+++ b/cont.c
@@ -1977,6 +1977,18 @@ fiber_to_s(VALUE fibval)
     return rb_block_to_s(fibval, &proc->block, status_info);
 }
 
+#ifdef HAVE_WORKING_FORK
+void
+rb_fiber_atfork(rb_thread_t *th)
+{
+    if (&th->root_fiber->cont.saved_ec != th->ec) {
+        th->root_fiber = th->ec->fiber_ptr;
+        th->root_fiber->cont.type = ROOT_FIBER_CONTEXT;
+    }
+    th->root_fiber->prev = 0;
+}
+#endif
+
 /*
  *  Document-class: FiberError
  *
diff --git a/test/ruby/test_fiber.rb b/test/ruby/test_fiber.rb
index ef7790b53c..c835246fda 100644
--- a/test/ruby/test_fiber.rb
+++ b/test/ruby/test_fiber.rb
@@ -269,7 +269,11 @@ class TestFiber < Test::Unit::TestCase
     end
     bug5700 = '[ruby-core:41456]'
     assert_nothing_raised(bug5700) do
-      Fiber.new{ pid = fork {} }.resume
+      Fiber.new do
+        pid = fork do
+          Fiber.new {}.transfer
+        end
+      end.resume
     end
     pid, status = Process.waitpid2(pid)
     assert_equal(0, status.exitstatus, bug5700)
diff --git a/thread.c b/thread.c
index 066d34c42a..e40b120f72 100644
--- a/thread.c
+++ b/thread.c
@@ -4381,6 +4381,7 @@ terminate_atfork_i(rb_thread_t *th, const rb_thread_t *current_th)
 
 /* mjit.c */
 void mjit_child_after_fork(void);
+void rb_fiber_atfork(rb_thread_t *);
 void
 rb_thread_atfork(void)
 {
@@ -4388,6 +4389,7 @@ rb_thread_atfork(void)
     rb_thread_atfork_internal(th, terminate_atfork_i);
     th->join_list = NULL;
     rb_mutex_cleanup_keeping_mutexes(th);
+    rb_fiber_atfork(th);
 
     /* We don't want reproduce CVE-2003-0900. */
     rb_reset_random_seed();