linux-kernel - Re: [RFC PATCH] mutex: Documentation rewrite

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Date:	Wed, 21 May 2014 12:02:56 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, paulmck@...ux.vnet.ibm.com,
	hpa@...or.com, waiman.long@...com, jason.low2@...com, aswin@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mutex: Documentation rewrite

On Wed, 2014-05-21 at 10:41 -0700, Davidlohr Bueso wrote:
> From: Davidlohr Bueso <davidlohr@...com>
> 
> Our mutexes have gone a long ways since the original implementation
> back in 2005/2006. However, the mutex-design.txt document is still
> stuck in the past, to the point where most of the information there
> is practically useless and, more important, simply incorrect. This
> patch pretty much rewrites it to resemble what we have nowadays.
> 
> Since regular semaphores are almost much extinct in the kernel
> (most users now rely on mutexes or rwsems), it no longer makes
> sense to have such a close comparison, which was copied from most
> of the cover letter when Ingo introduced the generic mutex subsystem.
> 
> While users who really want to learn more about kernel mutexes can
> go and read the code, I have marked this RFC since I'm sure more gory
> details can be included. Also, ww_mutexes are intentionally left out,
> leaving things as generic as possible.
> 
> Comments welcome!

Thanks for doing this.

> +
> +(iii) slowpath: last resource, if the lock is still unable to be acquired

change "last resource" to "last resort"


>  
>  Disadvantages
>  -------------
>  
> -The stricter mutex API means you cannot use mutexes the same way you
> -can use semaphores: e.g. they cannot be used from an interrupt context,
> -nor can they be unlocked from a different context that which acquired
> -it. [ I'm not aware of any other (e.g. performance) disadvantages from
> -using mutexes at the moment, please let me know if you find any. ]
> -

Should we keep this instead of deleting it?  It is still true we
cannot use mutex from an interrupt context.

Tim

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