Date: Thu, 13 Dec 2007 20:39:56 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Matthew Wilcox <matthew@wil.cx>
Cc: Roland McGrath <roland@redhat.com>, Petr Tesarik <ptesarik@suse.cz>,
       Tony Luck <tony.luck@intel.com>, Matthew Wilcox <willy@debian.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arch_ptrace_stop
Message-ID: <20071213173956.GA436@tv-sign.ru>
References: <20071213172926.GA423@tv-sign.ru> <20071213173136.GO26334@parisc-linux.org>
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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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