linux-kernel - Re: [PATCH 1/2] tsc2007: remove HR timer

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Date:	Thu, 09 Jul 2009 18:51:56 +0200
From:	Richard Röjfors 
	<richard.rojfors.ext@...ean-labs.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	kwangwoo.lee@...il.com, thierry.reding@...onic-design.de,
	soni.trilok@...il.com
Subject: Re: [PATCH 1/2] tsc2007: remove HR timer

On 6/25/09 11:20 PM, Andrew Morton wrote:
> On Tue, 23 Jun 2009 13:54:48 +0200
> Richard R__jfors<richard.rojfors.ext@...ean-labs.com>  wrote:
>
>> This patch removes the HR timer, since it's bad to do synchronous I2C
>> in the HR timer callback context. The new implementation makes use
>> of the global workqueue. The work is scheduled every 5ms when polling
>> rather than 5 us.
>>
>
> "it's bad" isn't a very good description of the problem which the patch
> fixes.

The problem is that the synchronous I2C calls in HR-timer callback 
context might end up in a deadlock.

>
> This matters.  People wish to make decisions about whether this patch
> is needed in 2.6.29.x, 2.6.30.x, 2.6.31, 2.6.32, etc.  Without knowing
> the effects of the problem which the patch fixes, we cannot make that
> decision!
>
>> +	/* cancel any work */
>> +	cancel_delayed_work(&ts->work);
>> +
>
> Should this have been cancel_delayed_work_sync()?

It should, I will post a new patch shortly which should be applied after 
these two which fixes this.

--Richard
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