diff options
| -rw-r--r-- | pkg/sentry/syscalls/linux/sys_futex.go | 10 | ||||
| -rw-r--r-- | test/syscalls/linux/futex.cc | 21 |
2 files changed, 31 insertions, 0 deletions
diff --git a/pkg/sentry/syscalls/linux/sys_futex.go b/pkg/sentry/syscalls/linux/sys_futex.go index b9bd25464..bde17a767 100644 --- a/pkg/sentry/syscalls/linux/sys_futex.go +++ b/pkg/sentry/syscalls/linux/sys_futex.go @@ -226,6 +226,11 @@ func Futex(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall if mask == 0 { return 0, nil, syserror.EINVAL } + if val <= 0 { + // The Linux kernel wakes one waiter even if val is + // non-positive. + val = 1 + } n, err := t.Futex().Wake(t, addr, private, mask, val) return uintptr(n), nil, err @@ -242,6 +247,11 @@ func Futex(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall case linux.FUTEX_WAKE_OP: op := uint32(val3) + if val <= 0 { + // The Linux kernel wakes one waiter even if val is + // non-positive. + val = 1 + } n, err := t.Futex().WakeOp(t, addr, naddr, private, val, nreq, op) return uintptr(n), nil, err 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<int> 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<int> a = ATOMIC_VAR_INIT(kInitialValue); |