linux-kernel - Re: [PATCH 0/8] make vfork killable/restartable/traceable

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Message-ID: <20110810214444.GD9320@atrey.karlin.mff.cuni.cz>
Date:	Wed, 10 Aug 2011 23:44:44 +0200
From:	Pavel Machek <pavel@....cz>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...k.frob.com>,
	Tejun Heo <tj@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Matt Fleming <matt.fleming@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] make vfork killable/restartable/traceable

Hi!

> CLONE_VFORK sleeps in TASK_INTERRUPTIBLE until the child exits/execs.
> This is obviously not good, it is sooo simple to create the task which
> doesn't react to SIGKILL/SIGSTOP.
> 
> Questions:
> 
> 	- do we really need this?
> 
> 	  I think we do. This really "looks like a bug" in any case,
> 	  even if nobody ever complained afaik.
> 
> 	- may be 1-3 is enough?
> 
> 	  may be... but personally I think SIGSTOP/ptrace should work
> 	  too.
> 
> 	- is it safe to exit/stop on !x86 machine???
> 
> 	  I do not know. May be this needs some #ifdef's around
> 	  wait_for_completion_interruptible(). I am not sure that,
> 	  say, arch_ptrace_stop() can't abuse the ->mm shared with
> 	  the child.
> 
> 	  OTOH. This can happen anyway, do_fork() does ptrace_event()
> 	  before wait_for_completion().
> 
> 	- and of course, while I think this is bugfix, this is user
> 	  visible change.
> 
> Please comment.

I believe we should fix it. I was always claiming "if it does not
react to SIGKILL, it is a kernel bug" and well, this just proved me
wrong...
									Pavel

-- 
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