rt: Don't limit the amount of stack available during unwinding. Closes #2144

Author: brson

src/rt/rust_task.cpp

@@ -514,7 +514,17 @@ rust_task::new_stack(size_t requested_sz) {
 
     if (total_stack_sz + rust_stk_sz > kernel->env->max_stack_size) {
         LOG_ERR(this, task, "task %" PRIxPTR " ran out of stack", this);
-        fail();
+        if (!unwinding) {
+            fail();
+        } else {
+            // FIXME: Because we have landing pads that may need more
+            // stack than normally allowed we have to go allow the stack
+            // to grow unbounded during unwinding. Would be nice to
+            // have a different solution - maybe just double the limit.
+            LOG_ERR(this, task, "task %" PRIxPTR " has blown its stack "
+                    "budget but we are unwinding so growing the stack "
+                    "anyway");
+        }
     }
 
     size_t sz = rust_stk_sz + RED_ZONE_SIZE;

src/test/run-fail/issue-2144.rs

@@ -0,0 +1,9 @@
+// error-pattern:ran out of stack
+
+// Don't leak when the landing pads need to request more stack
+// than is allowed during normal execution
+
+fn useBlock(f: fn~() -> uint) { useBlock({|| 22u }) }
+fn main() {
+    useBlock({|| 22u });
+}