1 files changed, 268 insertions, 0 deletions
diff --git a/test/syscalls/linux/membarrier.cc b/test/syscalls/linux/membarrier.cc
new file mode 100644
index 000000000..516956a25
--- /dev/null
+++ b/test/syscalls/linux/membarrier.cc
@@ -0,0 +1,268 @@
+// Copyright 2020 The gVisor Authors.
+//
+// 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 <errno.h>
+#include <signal.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <atomic>
+
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+#include "test/util/cleanup.h"
+#include "test/util/logging.h"
+#include "test/util/memory_util.h"
+#include "test/util/posix_error.h"
+#include "test/util/test_util.h"
+#include "test/util/thread_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+// This is the classic test case for memory fences on architectures with total
+// store ordering; see e.g. Intel SDM Vol. 3A Sec. 8.2.3.4 "Loads May Be
+// Reordered with Earlier Stores to Different Locations". In each iteration of
+// the test, given two variables X and Y initially set to 0
+// (MembarrierTestSharedState::local_var and remote_var in the code), two
+// threads execute as follows:
+//
+// T1                                   T2
+// --                                   --
+//
+// X = 1                                Y = 1
+// T1fence()                            T2fence()
+// read Y                               read X
+//
+// On architectures where memory writes may be locally buffered by each CPU
+// (essentially all architectures), if T1fence() and T2fence() are omitted or
+// ineffective, it is possible for both T1 and T2 to read 0 because the memory
+// write from the other CPU is not yet visible outside that CPU. T1fence() and
+// T2fence() are expected to perform the necessary synchronization to restore
+// sequential consistency: both threads agree on a order of memory accesses that
+// is consistent with program order in each thread, such that at least one
+// thread reads 1.
+//
+// In the NoMembarrier test, T1fence() and T2fence() are both ordinary memory
+// fences establishing ordering between memory accesses before and after the
+// fence (std::atomic_thread_fence). In all other test cases, T1fence() is not a
+// memory fence at all, but only prevents compiler reordering of memory accesses
+// (std::atomic_signal_fence); T2fence() is an invocation of the membarrier()
+// syscall, which establishes ordering of memory accesses before and after the
+// syscall on both threads.
+
+template <typename F>
+int DoMembarrierTestSide(std::atomic<int>* our_var,
+                         std::atomic<int> const& their_var,
+                         F const& test_fence) {
+  our_var->store(1, std::memory_order_relaxed);
+  test_fence();
+  return their_var.load(std::memory_order_relaxed);
+}
+
+struct MembarrierTestSharedState {
+  std::atomic<int64_t> remote_iter_cur;
+  std::atomic<int64_t> remote_iter_done;
+  std::atomic<int> local_var;
+  std::atomic<int> remote_var;
+  int remote_obs_of_local_var;
+
+  void Init() {
+    remote_iter_cur.store(-1, std::memory_order_relaxed);
+    remote_iter_done.store(-1, std::memory_order_relaxed);
+  }
+};
+
+// Special value for MembarrierTestSharedState::remote_iter_cur indicating that
+// the remote thread should terminate.
+constexpr int64_t kRemoteIterStop = -2;
+
+// Must be async-signal-safe.
+template <typename F>
+void RunMembarrierTestRemoteSide(MembarrierTestSharedState* state,
+                                 F const& test_fence) {
+  int64_t i = 0;
+  int64_t cur;
+  while (true) {
+    while ((cur = state->remote_iter_cur.load(std::memory_order_acquire)) < i) {
+      if (cur == kRemoteIterStop) {
+        return;
+      }
+      // spin
+    }
+    state->remote_obs_of_local_var =
+        DoMembarrierTestSide(&state->remote_var, state->local_var, test_fence);
+    state->remote_iter_done.store(i, std::memory_order_release);
+    i++;
+  }
+}
+
+template <typename F>
+void RunMembarrierTestLocalSide(MembarrierTestSharedState* state,
+                                F const& test_fence) {
+  // On test completion, instruct the remote thread to terminate.
+  Cleanup cleanup_remote([&] {
+    state->remote_iter_cur.store(kRemoteIterStop, std::memory_order_relaxed);
+  });
+
+  int64_t i = 0;
+  absl::Time end = absl::Now() + absl::Seconds(5);  // arbitrary test duration
+  while (absl::Now() < end) {
+    // Reset both vars to 0.
+    state->local_var.store(0, std::memory_order_relaxed);
+    state->remote_var.store(0, std::memory_order_relaxed);
+    // Instruct the remote thread to begin this iteration.
+    state->remote_iter_cur.store(i, std::memory_order_release);
+    // Perform our side of the test.
+    auto local_obs_of_remote_var =
+        DoMembarrierTestSide(&state->local_var, state->remote_var, test_fence);
+    // Wait for the remote thread to finish this iteration.
+    while (state->remote_iter_done.load(std::memory_order_acquire) < i) {
+      // spin
+    }
+    ASSERT_TRUE(local_obs_of_remote_var != 0 ||
+                state->remote_obs_of_local_var != 0);
+    i++;
+  }
+}
+
+TEST(MembarrierTest, NoMembarrier) {
+  MembarrierTestSharedState state;
+  state.Init();
+
+  ScopedThread remote_thread([&] {
+    RunMembarrierTestRemoteSide(
+        &state, [] { std::atomic_thread_fence(std::memory_order_seq_cst); });
+  });
+  RunMembarrierTestLocalSide(
+      &state, [] { std::atomic_thread_fence(std::memory_order_seq_cst); });
+}
+
+enum membarrier_cmd {
+  MEMBARRIER_CMD_QUERY = 0,
+  MEMBARRIER_CMD_GLOBAL = (1 << 0),
+  MEMBARRIER_CMD_GLOBAL_EXPEDITED = (1 << 1),
+  MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED = (1 << 2),
+  MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
+  MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
+};
+
+int membarrier(membarrier_cmd cmd, int flags) {
+  return syscall(SYS_membarrier, cmd, flags);
+}
+
+PosixErrorOr<int> SupportedMembarrierCommands() {
+  int cmds = membarrier(MEMBARRIER_CMD_QUERY, 0);
+  if (cmds < 0) {
+    if (errno == ENOSYS) {
+      // No commands are supported.
+      return 0;
+    }
+    return PosixError(errno, "membarrier(MEMBARRIER_CMD_QUERY) failed");
+  }
+  return cmds;
+}
+
+TEST(MembarrierTest, Global) {
+  SKIP_IF((ASSERT_NO_ERRNO_AND_VALUE(SupportedMembarrierCommands()) &
+           MEMBARRIER_CMD_GLOBAL) == 0);
+
+  Mapping m = ASSERT_NO_ERRNO_AND_VALUE(
+      MmapAnon(kPageSize, PROT_READ | PROT_WRITE, MAP_SHARED));
+  auto state = static_cast<MembarrierTestSharedState*>(m.ptr());
+  state->Init();
+
+  pid_t const child_pid = fork();
+  if (child_pid == 0) {
+    // In child process.
+    RunMembarrierTestRemoteSide(
+        state, [] { TEST_PCHECK(membarrier(MEMBARRIER_CMD_GLOBAL, 0) == 0); });
+    _exit(0);
+  }
+  // In parent process.
+  ASSERT_THAT(child_pid, SyscallSucceeds());
+  Cleanup cleanup_child([&] {
+    int status;
+    ASSERT_THAT(waitpid(child_pid, &status, 0),
+                SyscallSucceedsWithValue(child_pid));
+    EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+        << " status " << status;
+  });
+  RunMembarrierTestLocalSide(
+      state, [] { std::atomic_signal_fence(std::memory_order_seq_cst); });
+}
+
+TEST(MembarrierTest, GlobalExpedited) {
+  constexpr int kRequiredCommands = MEMBARRIER_CMD_GLOBAL_EXPEDITED |
+                                    MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED;
+  SKIP_IF((ASSERT_NO_ERRNO_AND_VALUE(SupportedMembarrierCommands()) &
+           kRequiredCommands) != kRequiredCommands);
+
+  ASSERT_THAT(membarrier(MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, 0),
+              SyscallSucceeds());
+
+  Mapping m = ASSERT_NO_ERRNO_AND_VALUE(
+      MmapAnon(kPageSize, PROT_READ | PROT_WRITE, MAP_SHARED));
+  auto state = static_cast<MembarrierTestSharedState*>(m.ptr());
+  state->Init();
+
+  pid_t const child_pid = fork();
+  if (child_pid == 0) {
+    // In child process.
+    RunMembarrierTestRemoteSide(state, [] {
+      TEST_PCHECK(membarrier(MEMBARRIER_CMD_GLOBAL_EXPEDITED, 0) == 0);
+    });
+    _exit(0);
+  }
+  // In parent process.
+  ASSERT_THAT(child_pid, SyscallSucceeds());
+  Cleanup cleanup_child([&] {
+    int status;
+    ASSERT_THAT(waitpid(child_pid, &status, 0),
+                SyscallSucceedsWithValue(child_pid));
+    EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0)
+        << " status " << status;
+  });
+  RunMembarrierTestLocalSide(
+      state, [] { std::atomic_signal_fence(std::memory_order_seq_cst); });
+}
+
+TEST(MembarrierTest, PrivateExpedited) {
+  constexpr int kRequiredCommands = MEMBARRIER_CMD_PRIVATE_EXPEDITED |
+                                    MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED;
+  SKIP_IF((ASSERT_NO_ERRNO_AND_VALUE(SupportedMembarrierCommands()) &
+           kRequiredCommands) != kRequiredCommands);
+
+  ASSERT_THAT(membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0),
+              SyscallSucceeds());
+
+  MembarrierTestSharedState state;
+  state.Init();
+
+  ScopedThread remote_thread([&] {
+    RunMembarrierTestRemoteSide(&state, [] {
+      TEST_PCHECK(membarrier(MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0) == 0);
+    });
+  });
+  RunMembarrierTestLocalSide(
+      &state, [] { std::atomic_signal_fence(std::memory_order_seq_cst); });
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor