Register custom stack for signal handlers

Summary: This updates FiberManager to automatically register custom stack for signal handlers. This ensures signal handlers will work correctly not only in case of stack overflow, but also if fiber stack size is just not enough for them.

Reviewed By: yfeldblum

Differential Revision: D3289912

fbshipit-source-id: 44959b727f70e1f1748d837b1a06c7414433e5ec

folly/experimental/fibers/FiberManager-inl.h

@@ -164,6 +164,10 @@ inline void FiberManager::runReadyFiber(Fiber* fiber) {
 }
 
 inline bool FiberManager::loopUntilNoReady() {
+  if (UNLIKELY(!alternateSignalStackRegistered_)) {
+    registerAlternateSignalStack();
+  }
+
   // Support nested FiberManagers
   auto originalFiberManager = this;
   std::swap(currentFiberManager_, originalFiberManager);

folly/experimental/fibers/FiberManager.cpp

@@ -15,6 +15,7 @@
  */
 #include "FiberManager.h"
 
+#include <signal.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
@@ -26,6 +27,8 @@
 #include <folly/experimental/fibers/Fiber.h>
 #include <folly/experimental/fibers/LoopController.h>
 
+#include <folly/SingletonThreadLocal.h>
+
 #ifdef FOLLY_SANITIZE_ADDRESS
 
 #include <dlfcn.h>
@@ -273,5 +276,62 @@ static AsanUnpoisonMemoryRegionFuncPtr getUnpoisonMemoryRegionFunc() {
 }
 
 #endif // FOLLY_SANITIZE_ADDRESS
+
+namespace {
+
+// SIGSTKSZ (8 kB on our architectures) isn't always enough for
+// folly::symbolizer, so allocate 32 kB.
+constexpr size_t kAltStackSize = folly::constexpr_max(SIGSTKSZ, 32 * 1024);
+
+bool hasAlternateStack() {
+  stack_t ss;
+  sigaltstack(nullptr, &ss);
+  return !(ss.ss_flags & SS_DISABLE);
+}
+
+int setAlternateStack(char* sp, size_t size) {
+  CHECK(sp);
+  stack_t ss{};
+  ss.ss_sp = sp;
+  ss.ss_size = size;
+  return sigaltstack(&ss, nullptr);
+}
+
+int unsetAlternateStack() {
+  stack_t ss{};
+  ss.ss_flags = SS_DISABLE;
+  return sigaltstack(&ss, nullptr);
+}
+
+class ScopedAlternateSignalStack {
+ public:
+  ScopedAlternateSignalStack() {
+    if (hasAlternateStack()) {
+      return;
+    }
+
+    stack_ = folly::make_unique<AltStackBuffer>();
+
+    setAlternateStack(stack_->data(), stack_->size());
+  }
+
+  ~ScopedAlternateSignalStack() {
+    if (stack_) {
+      unsetAlternateStack();
+    }
+  }
+
+ private:
+  using AltStackBuffer = std::array<char, kAltStackSize>;
+  std::unique_ptr<AltStackBuffer> stack_;
+};
+}
+
+void FiberManager::registerAlternateSignalStack() {
+  static folly::SingletonThreadLocal<ScopedAlternateSignalStack> singleton;
+  singleton.get();
+
+  alternateSignalStackRegistered_ = true;
+}
 }
 }

folly/experimental/fibers/FiberManager.h

@@ -467,6 +467,10 @@ class FiberManager : public ::folly::Executor {
   void unpoisonFiberStack(const Fiber* fiber);
 
 #endif // FOLLY_SANITIZE_ADDRESS
+
+  bool alternateSignalStackRegistered_{false};
+
+  void registerAlternateSignalStack();
 };
 
 /**

folly/experimental/fibers/test/StackOverflow.cpp

+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include <folly/experimental/fibers/FiberManagerMap.h>
+#include <folly/experimental/symbolizer/SignalHandler.h>
+#include <folly/init/Init.h>
+
+void f(int* p) {
+  // Make sure recursion is not optimized out
+  int a[100];
+  for (size_t i = 0; i < 100; ++i) {
+    a[i] = i;
+    ++(a[i]);
+    if (p) {
+      a[i] += p[i];
+    }
+  }
+  f(a);
+}
+
+int main(int argc, char* argv[]) {
+  folly::init(&argc, &argv);
+
+  folly::EventBase evb;
+  folly::fibers::getFiberManager(evb).addTask([&]() { f(nullptr); });
+  evb.loop();
+}