linux-kernel - Re: [PATCH 09/18] lirc driver for the Streamzap PC Receiver

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Message-ID: <20080911092226.2605a96a@bike.lwn.net>
Date:	Thu, 11 Sep 2008 09:22:26 -0600
From:	Jonathan Corbet <corbet@....net>
To:	unlisted-recipients:; (no To-header on input)
Cc:	linux-kernel@...r.kernel.org, Jarod Wilson <jwilson@...hat.com>,
	Janne Grunau <j@...nau.net>,
	Christoph Bartelmus <lirc@...telmus.de>
Subject: Re: [PATCH 09/18] lirc driver for the Streamzap PC Receiver

[Yes, you said I shouldn't do more reviews of the posted code, but the
following was already pretty much written.  I really only found one thing
in this driver, and I suspect it may not have been addressed yet.  

This was set to be the last anyway, I'm pretty much out of time for now.]

jon

I'm curious about the following function:

> +static void stop_timer(struct usb_streamzap *sz)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&sz->timer_lock, flags);
> +	if (sz->timer_running) {

What happens if the timer fires right here?  

> +		sz->timer_running = 0;
> +		del_timer_sync(&sz->delay_timer);
> +	}
> +	spin_unlock_irqrestore(&sz->timer_lock, flags);
> +}

The timer acquires the lock too, so this looks a bit like a deadlock to
me.  Probably del_timer_sync() should be called without the lock?
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