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 --- pkg/sentry/syscalls/linux/sys_futex.go | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'pkg/sentry') 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 -- cgit v1.2.3