signal.c: drop dangerous tag

* signal.c (check_stack_overflow): drop the last tag too close to
  the fault page, to get rid of stack overflow deadlock.
  [Bug #9971]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46499 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 12 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 4b0fb2c4fc..070269ad6a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Jun 23 11:11:16 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* signal.c (check_stack_overflow): drop the last tag too close to
+	  the fault page, to get rid of stack overflow deadlock.
+	  [Bug #9971]
+
 Sun Jun 22 09:11:15 2014  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/uri/generic.rb: remove registry.
diff --git a/signal.c b/signal.c
index 1833639352..f49bd2aabf 100644
--- a/signal.c
+++ b/signal.c
@@ -738,6 +738,12 @@ check_stack_overflow(const uintptr_t addr, const ucontext_t *ctx)
      * the fault page can be the next. */
     if (sp_page == fault_page || sp_page == fault_page + 1) {
 	rb_thread_t *th = ruby_current_thread;
+	if ((uintptr_t)th->tag->buf / pagesize == sp_page) {
+	    /* drop the last tag if it is close to the fault,
+	     * otherwise it can cause stack overflow again at the same
+	     * place. */
+	    th->tag = th->tag->prev;
+	}
 	ruby_thread_stack_overflow(th);
     }
 }