linux-kernel - SIGNAL_UNKILLABLE and init again

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Message-ID: <20170425173928.gaubfmxxbbvglnio@cedar>
Date:   Tue, 25 Apr 2017 18:39:28 +0100
From:   Jamie Iles <jamie.iles@...cle.com>
To:     Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org
Subject: SIGNAL_UNKILLABLE and init again

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