linux-kernel - Re: [PATCH 1/3] pda_power: add support for writeable properties

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Date:	Tue, 11 May 2010 22:23:47 +0400
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Daniel Mack <daniel@...aq.de>
Cc:	linux-kernel@...r.kernel.org,
	David Woodhouse <dwmw2@...radead.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Len Brown <len.brown@...el.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Matt Reimer <mreimer@...p.net>,
	Evgeniy Polyakov <zbr@...emap.net>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 1/3] pda_power: add support for writeable properties

On Tue, May 11, 2010 at 07:58:12PM +0200, Daniel Mack wrote:
[...]
> Hmm, no. The code defaults to (S_IRUSR | S_IRGRP | S_IROTH) which is
> 0444, just like it was before. So there shouldn't be any regression. The
> mode is only changed if the psy defines a property_is_writeable()
> callback which returns 1. Or do I miss your point?

Yes, power_supply_attrs is a global array, and you shouldn't change
it between power_supply_register() calls.

If you don't see why it's a bad idea in general, think about it
other way, a race:

...someone registers psy0 with attr X marked as read-only...
...code flow stops before device_create_file(psy0, global->mode)..
[preempt]
...someone registers psy1 with attr X marked as writable...
...you set up global->mode to 0644...
[preempt again]
...we end up calling device_create_file(psy0, 0644)...

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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