linux-kernel - Re: V4L2 drivers: potentially dangerous and inefficient msecs_to

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Message-ID: <20090914213933.GA5468@rhlx01.hs-esslingen.de>
Date:	Mon, 14 Sep 2009 23:39:33 +0200
From:	Andreas Mohr <andi@...as.de>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Andreas Mohr <andi@...as.de>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Luca Risolia <luca.risolia@...dio.unibo.it>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: V4L2 drivers: potentially dangerous and inefficient
	msecs_to_jiffies() calculation

Hi,

On Mon, Sep 14, 2009 at 11:34:40PM +0200, Jiri Slaby wrote:
> On 09/14/2009 11:07 PM, Andreas Mohr wrote:
> > ./drivers/media/video/zc0301/zc0301_core.c
> > do
> >                             cam->module_param.frame_timeout *
> >                             1000 * msecs_to_jiffies(1) );
> > multiple times each.
> > What they should do instead is
> > frame_timeout * msecs_to_jiffies(1000), I'd think.
> 
> In fact, msecs_to_jiffies(frame_timeout * 1000) makes much more sense.

Heh, right, even a bit better ;)

> > msecs_to_jiffies(1) is quite a bit too boldly assuming
> > that all of the msecs_to_jiffies(x) implementation branches
> > always round up.
> 
> They do, don't they?

I'd hope so, but a slight risk remains, you never know,
especially with 4+ or so variants...

Andreas Mohr
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