linux-kernel - Re: [RFC] mmiotrace full patch, preview 1

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Message-ID: <20080225214200.yge03wi7ksoccw0k@webmail.spamcop.net>
Date:	Mon, 25 Feb 2008 21:42:00 -0500
From:	Pavel Roskin <proski@....org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Paalanen <pq@....fi>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Whitcroft <apw@...dowen.org>
Subject: Re: [RFC] mmiotrace full patch, preview 1

Quoting Christoph Hellwig <hch@...radead.org>:

> On Mon, Feb 25, 2008 at 02:49:22PM -0800, Andrew Morton wrote:
>> the things which it finds.
>>
>> > +static DECLARE_MUTEX(kmmio_init_mutex);
>>
>> That's not a mutex.
>>
>> > +	down(&kmmio_init_mutex);
>>
>> It's a semaphore.  Please do convert it to a mutex.
>>
>> Andy, I'd say that addition of new semaphores is worth a warning - they're
>> rarely legitimate.
>
> I'm not sure that any semaphore should be a warning, but the initializer
> for semaphore used as binary mutex (DECLARE_MUTEX and init_MUTEX) are
> worth it.

It looks like a mutex, it acts like a mutex, but it isn't a mutex,  
it's a trap for the unwary.  Weird.  I was annoyed by it before; now I  
see a fellow developer actually getting into that trap.

I'd say, rename DECLARE_MUTEX to DECLARE_SEMAPHORE and let external  
code be fixed one way or another (i.e. stick with the "mutex" name or  
stick with the semaphore functionality if it's really needed).

-- 
Regards,
Pavel Roskin
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