linux-kernel - Re: [PATCH] LinuxPPS

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Message-ID: <20070724160144.GG4074@enneenne.com>
Date:	Tue, 24 Jul 2007 18:01:44 +0200
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] LinuxPPS - definitive version

On Tue, Jul 24, 2007 at 03:52:49PM +0100, David Woodhouse wrote:
> 
> Elsewhere in the patch.

Got, thanks.

> Read Documentation/memory-barriers.txt
> 
> There is a tiny but possibly non-zero chance that one CPU could be in
> pps_event() and might not yet have 'seen' the change to the .info field.
> Releasing the pps_mutex provides a write-barrier on the CPU which runs
> pps_unregister_source(), but there's no corresponding read-barrier on
> the CPU running pps_event(). You have to be careful about when
> pps_event() is run. It _MUST_ not touch the old info structure after
> pps_unregister_source() has completed.
> 
> At the moment, I think it's OK because you won't be calling pps_event()
> at the wrong times. But you do need to make sure that requirement is
> documented. And I think you can remove the whole dummy_info thing
> because it's not necessary.

What about this new solution involving tasklets? The pps_event() now
just records data and then a tasklet do the data management job. :)

Ciao,

Rodolfo

-- 

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