thread_pthread.c: Fix intermittent SIGBUS on Linux

* thread_pthread.c (reserve_stack): fix intermittent SIGBUS on
  Linux, by reserving the stack virtual address space at process
  start up so that it will not clash with the heap space.
  [Fix GH-822]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49452 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,10 @@
+Sat Jan 31 12:06:23 2015  Scott Francis  <scott.francis@shopify.com>
+
+	* thread_pthread.c (reserve_stack): fix intermittent SIGBUS on
+	  Linux, by reserving the stack virtual address space at process
+	  start up so that it will not clash with the heap space.
+	  [Fix GH-822]
+
 Fri Jan 30 17:28:29 2015  gogotanaka  <mail@tanakakazuki.com>
 
 	* math.c (num2dbl_with_to_f): make faster when Bignum passed by

thread_pthread.c

@@ -653,6 +653,42 @@ space_size(size_t stack_size)
     }
 }
 
+#ifdef __linux__
+static __attribute__((noinline)) void
+reserve_stack(volatile char *limit, size_t size)
+{
+# ifdef C_ALLOCA
+#   error needs alloca()
+# endif
+    struct rlimit rl;
+    volatile char buf[0x100];
+    STACK_GROW_DIR_DETECTION;
+
+    if (!getrlimit(RLIMIT_STACK, &rl) && rl.rlim_cur == RLIM_INFINITY)
+	return;
+
+    size -= sizeof(buf); /* margin */
+    if (IS_STACK_DIR_UPPER()) {
+	const volatile char *end = buf + sizeof(buf);
+	limit += size;
+	if (limit > end) {
+	    size = limit - end;
+	    limit = alloca(size);
+	    limit[size-1] = 0;
+	}
+    }
+    else {
+	limit -= size;
+	if (buf > limit) {
+	    limit = alloca(buf - limit);
+	    limit[0] = 0;
+	}
+    }
+}
+#else
+# define reserve_stack(limit, size) ((void)(limit), (void)(size))
+#endif
+
 #undef ruby_init_stack
 /* Set stack bottom of Ruby implementation.
  *
@@ -674,6 +710,7 @@ ruby_init_stack(volatile VALUE *addr
 	if (get_main_stack(&stackaddr, &size) == 0) {
 	    native_main_thread.stack_maxsize = size;
 	    native_main_thread.stack_start = stackaddr;
+	    reserve_stack(stackaddr, size);
 	    return;
 	}
     }