linux-kernel - Re: SIGNAL_UNKILLABLE and init again

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Message-ID: <20170426151857.GA11894@redhat.com>
Date:   Wed, 26 Apr 2017 17:18:58 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jamie Iles <jamie.iles@...cle.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: SIGNAL_UNKILLABLE and init again

Hi Jamie,

On 04/25, Jamie Iles wrote:
>
> 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;

Yes, this is what I meant when I said force_sig_info() needs changes too.
I was going to fix it "tomorrow" but I was distracted and then forgot.

>   @@ -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);

Not sure, let me think a bit more... and this is not enough anyway.

perhaps we should start with this simple change, but the "real" fix
needs a lot of cleanups, although I am not sure if we will ever do this.

Oleg.