From 29955a4797e8264f75886a989dbc81b2b5443f4c Mon Sep 17 00:00:00 2001 From: Andrei Vagin Date: Thu, 19 Dec 2019 17:25:18 -0800 Subject: futex: wake one waiter if futex_wake is called with a non-positive value This change is needed to be compatible with the Linux kernel. There is no glibc wrapper for the futex system call, so it is easy to make a mistake and call syscall(__NR_futex, FUTEX_WAKE, addr) without the fourth argument. This works on Linux, because it wakes one waiter even if val is nonpositive. PiperOrigin-RevId: 286494396 --- test/syscalls/linux/futex.cc | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'test/syscalls/linux') diff --git a/test/syscalls/linux/futex.cc b/test/syscalls/linux/futex.cc index d3e3f998c..40c80a6e1 100644 --- a/test/syscalls/linux/futex.cc +++ b/test/syscalls/linux/futex.cc @@ -239,6 +239,27 @@ TEST_P(PrivateAndSharedFutexTest, Wake1_NoRandomSave) { EXPECT_THAT(futex_wake(IsPrivate(), &a, 1), SyscallSucceedsWithValue(1)); } +TEST_P(PrivateAndSharedFutexTest, Wake0_NoRandomSave) { + constexpr int kInitialValue = 1; + std::atomic a = ATOMIC_VAR_INIT(kInitialValue); + + // Prevent save/restore from interrupting futex_wait, which will cause it to + // return EAGAIN instead of the expected result if futex_wait is restarted + // after we change the value of a below. + DisableSave ds; + ScopedThread thread([&] { + EXPECT_THAT(futex_wait(IsPrivate(), &a, kInitialValue), + SyscallSucceedsWithValue(0)); + }); + absl::SleepFor(kWaiterStartupDelay); + + // Change a so that if futex_wake happens before futex_wait, the latter + // returns EAGAIN instead of hanging the test. + a.fetch_add(1); + // The Linux kernel wakes one waiter even if val is 0 or negative. + EXPECT_THAT(futex_wake(IsPrivate(), &a, 0), SyscallSucceedsWithValue(1)); +} + TEST_P(PrivateAndSharedFutexTest, WakeAll_NoRandomSave) { constexpr int kInitialValue = 1; std::atomic a = ATOMIC_VAR_INIT(kInitialValue); -- cgit v1.2.3