[cctest] Test SharedMutex plus sampling

The combination of pthread_rwlock_t and signals causes spurious
deadlocks on Mac (see linked issue).
This adds a cctest which tests this combination. This test is skipped on
Mac, where it would deadlock. This test can be used to document and
further investigate the issue, and test potential fixes.

R=jkummerow@chromium.org

Bug: v8:11399
Change-Id: I5d1fcdd84db253ec2d0637575239f212aae2ecb7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2856553Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74662}

test/cctest/BUILD.gn

@@ -173,6 +173,7 @@ v8_source_set("cctest_sources") {
     "interpreter/test-interpreter.cc",
     "interpreter/test-source-positions.cc",
     "libplatform/test-tracing.cc",
+    "libsampler/signals-and-mutexes.cc",
     "libsampler/test-sampler.cc",
     "manually-externalized-buffer.h",
     "parsing/test-parse-decision.cc",

test/cctest/cctest.status

@@ -118,7 +118,6 @@
   'test-local-handles/DereferenceLocalHandleFailsWhenDisallowed': [SKIP, ['mode == debug', FAIL]],
   'test-persistent-handles/DereferencePersistentHandleFailsWhenDisallowed': [SKIP, ['mode == debug', FAIL]],
 
-############################################################################
   # Slow tests.
   'test-debug/CallFunctionInDebugger': [PASS, ['mode == debug', SLOW]],
   'test-heap-profiler/ManyLocalsInSharedContext': [PASS, SLOW],
@@ -126,6 +125,9 @@
   'test-strings/StringOOM*': [PASS, ['mode == debug', SKIP]],
   'test-serialize/CustomSnapshotDataBlobImmortalImmovableRoots': [PASS, ['mode == debug', SKIP]],
   'test-parsing/ObjectRestNegativeTestSlow': [PASS, ['mode == debug', SKIP]],
+
+  # pthread_rwlock_t combined with signals is broken on Mac (https://crbug.com/v8/11399).
+  'signals-and-mutexes/SignalsPlusSharedMutexes': [PASS, ['system == macos', SKIP]],
 }],  # ALWAYS
 
 ##############################################################################

test/cctest/libsampler/signals-and-mutexes.cc

+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <signal.h>
+
+#include "src/base/platform/mutex.h"
+#include "src/base/platform/platform.h"
+#include "src/base/platform/time.h"
+#include "src/base/utils/random-number-generator.h"
+#include "src/libsampler/sampler.h"  // for USE_SIGNALS
+#include "test/cctest/cctest.h"
+
+namespace v8 {
+namespace sampler {
+
+// There seem to be problems with pthread_rwlock_t and signal handling on
+// Mac, see https://crbug.com/v8/11399 and
+// https://stackoverflow.com/questions/22643374/deadlock-with-pthread-rwlock-t-and-signals
+// This test reproduces it, and can be used to test if this problem is fixed in
+// future Mac releases.
+
+#ifdef USE_SIGNALS
+
+void HandleProfilerSignal(int signal, siginfo_t*, void*) {
+  CHECK_EQ(SIGPROF, signal);
+}
+
+struct sigaction old_signal_handler;
+
+void InstallSignalHandler() {
+  struct sigaction sa;
+  sa.sa_sigaction = &HandleProfilerSignal;
+  sigemptyset(&sa.sa_mask);
+  sa.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
+  CHECK_EQ(0, sigaction(SIGPROF, &sa, &old_signal_handler));
+}
+
+static void RestoreSignalHandler() {
+  sigaction(SIGPROF, &old_signal_handler, nullptr);
+}
+
+TEST(SignalsPlusSharedMutexes) {
+  static constexpr int kNumMutexes = 1024;
+  // 10us * 10000 = 100ms
+  static constexpr auto kSleepBetweenSamples =
+      base::TimeDelta::FromMicroseconds(10);
+  static constexpr size_t kNumSamples = 10000;
+
+  // Keep a set of all currently running threads. This is filled by the threads
+  // themselves, because we need to get their pthread id.
+  base::Mutex threads_mutex;
+  std::set<pthread_t> threads_to_sample;
+  auto SendSignalToThreads = [&threads_mutex, &threads_to_sample] {
+    base::MutexGuard guard(&threads_mutex);
+    for (pthread_t tid : threads_to_sample) {
+      pthread_kill(tid, SIGPROF);
+    }
+  };
+  auto AddThreadToSample = [&threads_mutex, &threads_to_sample](pthread_t tid) {
+    base::MutexGuard guard(&threads_mutex);
+    CHECK(threads_to_sample.insert(tid).second);
+  };
+  auto RemoveThreadToSample = [&threads_mutex,
+                               &threads_to_sample](pthread_t tid) {
+    base::MutexGuard guard(&threads_mutex);
+    CHECK_EQ(1, threads_to_sample.erase(tid));
+  };
+
+  // The sampling threads periodically sends a SIGPROF to all running threads.
+  class SamplingThread : public base::Thread {
+   public:
+    explicit SamplingThread(std::atomic<size_t>* remaining_samples,
+                            std::function<void()> send_signal_to_threads)
+        : Thread(base::Thread::Options{"SamplingThread"}),
+          remaining_samples_(remaining_samples),
+          send_signal_to_threads_(std::move(send_signal_to_threads)) {}
+
+    void Run() override {
+      DCHECK_LT(0, remaining_samples_->load(std::memory_order_relaxed));
+      while (remaining_samples_->fetch_sub(1, std::memory_order_relaxed) > 1) {
+        send_signal_to_threads_();
+        base::OS::Sleep(kSleepBetweenSamples);
+      }
+      DCHECK_EQ(0, remaining_samples_->load(std::memory_order_relaxed));
+    }
+
+   private:
+    std::atomic<size_t>* const remaining_samples_;
+    const std::function<void()> send_signal_to_threads_;
+  };
+
+  // These threads repeatedly lock and unlock a shared mutex, both in shared and
+  // exclusive mode. This should not deadlock.
+  class SharedMutexTestThread : public base::Thread {
+   public:
+    SharedMutexTestThread(
+        base::SharedMutex* mutexes, std::atomic<size_t>* remaining_samples,
+        int64_t rng_seed, std::function<void(pthread_t)> add_thread_to_sample,
+        std::function<void(pthread_t)> remove_thread_to_sample)
+        : Thread(Thread::Options{"SharedMutexTestThread"}),
+          mutexes_(mutexes),
+          remaining_samples_(remaining_samples),
+          rng_(rng_seed),
+          add_thread_to_sample_(add_thread_to_sample),
+          remove_thread_to_sample_(remove_thread_to_sample) {}
+
+    void Run() override {
+      add_thread_to_sample_(pthread_self());
+      while (remaining_samples_->load(std::memory_order_relaxed) > 0) {
+        size_t idx = rng_.NextInt(kNumMutexes);
+        base::SharedMutex* mutex = &mutexes_[idx];
+        if (rng_.NextBool()) {
+          base::SharedMutexGuard<base::kShared> guard{mutex};
+        } else {
+          base::SharedMutexGuard<base::kExclusive> guard{mutex};
+        }
+      }
+      remove_thread_to_sample_(pthread_self());
+    }
+
+   private:
+    base::SharedMutex* mutexes_;
+    std::atomic<size_t>* remaining_samples_;
+    base::RandomNumberGenerator rng_;
+    std::function<void(pthread_t)> add_thread_to_sample_;
+    std::function<void(pthread_t)> remove_thread_to_sample_;
+  };
+
+  std::atomic<size_t> remaining_samples{kNumSamples};
+  base::SharedMutex mutexes[kNumMutexes];
+
+  InstallSignalHandler();
+
+  auto* rng = CcTest::i_isolate()->random_number_generator();
+
+  // First start the mutex threads, then the sampling thread.
+  std::vector<std::unique_ptr<SharedMutexTestThread>> threads(4);
+  for (auto& thread : threads) {
+    thread = std::make_unique<SharedMutexTestThread>(
+        mutexes, &remaining_samples, rng->NextInt64(), AddThreadToSample,
+        RemoveThreadToSample);
+    CHECK(thread->Start());
+  }
+
+  SamplingThread sampling_thread(&remaining_samples, SendSignalToThreads);
+  CHECK(sampling_thread.Start());
+
+  // Wait for the sampling thread to be done. The mutex threads should finish
+  // shortly after.
+  sampling_thread.Join();
+  for (auto& thread : threads) thread->Join();
+
+  RestoreSignalHandler();
+}
+
+#endif  // USE_SIGNALS
+
+}  // namespace sampler
+}  // namespace v8