SIGNAL_UNKILLABLE and init again

[Jamie Iles]

Hi Oleg,

I'm back looking at SIGNAL_UNKILLABLE and debugging child reapers again, 
and the current issue is when running code in the target process, 
SIGTRAP firing and that causing SIGNAL_UNKILLABLE protection to be 
removed in force_sig_info():

        if (action->sa.sa_handler == SIG_DFL)
                t->signal->flags &= ~SIGNAL_UNKILLABLE;

Would relaxing that if the task is being traced with something like

  diff --git i/kernel/signal.c w/kernel/signal.c
  index 7e59ebc2c25e..f701f1889895 100644
  --- i/kernel/signal.c
  +++ w/kernel/signal.c
  @@ -1185,7 +1185,7 @@ force_sig_info(int sig, struct siginfo *info, struct 
task_struct *t)
                        recalc_sigpending_and_wake(t);
                }
        }
  -     if (action->sa.sa_handler == SIG_DFL)
  +     if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
                t->signal->flags &= ~SIGNAL_UNKILLABLE;
        ret = specific_send_sig_info(sig, info, t);
        spin_unlock_irqrestore(&t->sighand->siglock, flags);

make any sense?  It does address the issue that I'm seeing, but are 
there any downsides to doing so?

Thanks,

Jamie