linux-kernel - Re: [PATCH] arch_ptrace

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Message-ID: <20071213173956.GA436@tv-sign.ru>
Date:	Thu, 13 Dec 2007 20:39:56 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Roland McGrath <roland@...hat.com>,
	Petr Tesarik <ptesarik@...e.cz>,
	Tony Luck <tony.luck@...el.com>,
	Matthew Wilcox <willy@...ian.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch_ptrace_stop

On 12/13, Matthew Wilcox wrote:
>
> On Thu, Dec 13, 2007 at 08:29:26PM +0300, Oleg Nesterov wrote:
> > How is it possible that SIGKILL is blocked?
> 
> I *think* it's possible that kernel threads may block SIGKILL.
> And I think init (pid 1) gets SIGKILL blocked.

Yes. But this shouldn't matter because we can't ptrace them. /sbin/init
doesn't block SIGKILL, but it can't be ptraced either.

Also, SIGKILL is blocked only if kthread was created by kernel_thread() and
then it does daemonize(). kthread_create()'ed kthreads don't block SIGKILL
but ignore it. The latter behaviour is more correct, but we can't do the same
for kernel_thread() threads.

Oleg.

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