From: Ian Campbell <ijc@hellion.org.uk>
To: Bernd Petrovitsch <bernd@firmix.at>
Cc: linux-kernel@vger.kernel.org, Arjan van de Ven <arjan@infradead.org>,
       lgb@lgb.hu
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Content-Type: text/plain
Date: Wed, 11 Jan 2006 14:05:16 +0000
Message-Id: <1136988316.6517.8.camel@localhost.localdomain>
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Subject: Re: OT: fork(): parent or child should run first?
Sender: linux-kernel-owner@vger.kernel.org
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On Wed, 2006-01-11 at 14:55 +0100, Bernd Petrovitsch wrote:
> On Wed, 2006-01-11 at 13:49 +0000, Ian Campbell wrote:
> > On Wed, 2006-01-11 at 14:25 +0100, Bernd Petrovitsch wrote:
> > > Then this leaves the race if an old pid is reused in a newly created
> > > process before the last instances of that pid is cleaned up.
> > 
> > The PID won't be available to be re-used until the signal handler has
> > called waitpid() on it?
> 
> Yes.
> But ATM the signal handler calls waitpid() and stores the pid in a
> to-be-cleaned-pids array (at time X).
> The main loop at some time in the future (say at time X+N) walks through
> the to-be-cleaned-pids array and cleans them from the active-childs
> array.

yuk... I'd say the application is a bit dumb for calling waitpid before
it is actually prepared for the pid to be reclaimed. 

A possible solution would be to also defer the waitpid until the main
loop cleanup function, perhaps flagging the entry in the child array as
not-active between the signal and that time or moving the pid from the
active to an inactive array in the signal handler.

Ian.
-- 
Ian Campbell
Current Noise: Sloth - Into The Sun

To err is human,
To purr feline.
		-- Robert Byrne

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