linux-kernel - Re: [RFC][PATCH 3/7] lockdep: Annotate read/write states

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Message-ID: <1303143991.7181.38.camel@gandalf.stny.rr.com>
Date:	Mon, 18 Apr 2011 12:26:31 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 3/7] lockdep: Annotate read/write states

On Sun, 2011-04-17 at 11:45 +0200, Peter Zijlstra wrote:

> Currently the read/write status of a lock while it's acquired is denoted by a
> monotonically increasing variable where:
> 
>  0 - WRITE
>  1 - READ
>  2 - RECURSIVE READ
> 
> In this patch, we propose to modify this distinction from a monotonically
> increasing variable to a bit mask where:
> 
>  0x1 - WRITE
>  0x2 - READ
>  0x4 - RECURSIVE READ
> 


>  /*
> @@ -286,6 +287,15 @@ extern void lockdep_init_map(struct lock
>  
>  #define lockdep_set_novalidate_class(lock) \
>  	lockdep_set_class(lock, &__lockdep_no_validate__)
> +
> +/* lock_state bits */
> +#define _W_		0
> +#define _R_		(_W_ + 1)
> +#define _RR_		(_W_ + 2)
> +#define _FIRST_RR_	(_W_ + 3)

Eek!!! Please comment these. I hate trying to figure out what RR means.
If I did not read the change log, my first thought was "Round Robin".

Adding something like:

/*
 * lock_state bits:
 *   WRITE
 *   READ
 *   RECURSIVE_READ
 *   FIRST RECURSIVE_READ
 */

Above that would help tremendously. This code is obfuscated enough, we
need many more comments. (I plan on sending out patches to do this too).



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