Re: [PATCH 4/6] kernel: add support for TIF_NOTIFY_SIGNAL

Oleg Nesterov
2020-10-08T13:53:34Z

On 10/05, Jens Axboe wrote:
>
> static inline int signal_pending(struct task_struct *p)
> {
> +#ifdef TIF_NOTIFY_SIGNAL
> + /*
> + * TIF_NOTIFY_SIGNAL isn't really a signal, but it requires the same
> + * behavior in terms of ensuring that we break out of wait loops
> + * so that notify signal callbacks can be processed.
> + */
> + if (unlikely(test_tsk_thread_flag(p, TIF_NOTIFY_SIGNAL)))
> + return 1;
> +#endif
> return task_sigpending(p);
> }

perhaps we can add test_tsk_thread_mask() later...

> static inline void restore_saved_sigmask_unless(bool interrupted)
> {
> - if (interrupted)
> + if (interrupted) {
> +#ifdef TIF_NOTIFY_SIGNAL
> + WARN_ON(!test_thread_flag(TIF_SIGPENDING) &&
> + !test_thread_flag(TIF_NOTIFY_SIGNAL));
> +#else
> WARN_ON(!test_thread_flag(TIF_SIGPENDING));
> - else
> +#endif
> + } else {
> restore_saved_sigmask();
> + }

I'd suggest to simply do

- WARN_ON(!test_thread_flag(TIF_SIGPENDING));
+ WARN_ON(!signal_pending(current);

> --- a/kernel/entry/kvm.c
> +++ b/kernel/entry/kvm.c
> @@ -8,6 +8,9 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
> do {
> int ret;
>
> + if (ti_work & _TIF_NOTIFY_SIGNAL)
> + tracehook_notify_signal();

Can't really comment this change, but to me it would be more safe to
simply return -EINTR.

Or perhaps even better, treat _TIF_NOTIFY_SIGNAL and _TIF_SIGPENDING
equally:

- if (ti_work & _TIF_SIGPENDING) {
+ if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
kvm_handle_signal_exit(vcpu);
return -EINTR;

Oleg.