linux-kernel - Re: mutex ownership (was: Re: [PATCH 19/24] Unionfs: Helper macros/inlines)

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Date:	Tue, 9 Jan 2007 10:09:29 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	arjan <arjan@...radead.org>
Subject: Re: mutex ownership (was: Re: [PATCH 19/24] Unionfs: Helper macros/inlines)

Am Dienstag, 9. Januar 2007 10:02 schrieb Peter Zijlstra:
> On Mon, 2007-01-08 at 13:28 -0800, Andrew Morton wrote:
> 
> > Please use mutexes where possible.  Semaphores should only be used when
> > their counting feature is employed.  And, arguably, in situations where a
> > lock is locked and unlocked from different threads, because this presently
> > triggers mutex debugging warnings, although we should find a way of fixing
> > this in the mutex code.
> 
> Its a fundamental property of a mutex, not a shortcoming. A mutex has an
> owner, the one that takes and releases the resource. This allows things
> such as Priority Inheritance to boost owners.
> 
> 'fixing' this takes away much of what a mutex is.
> 
> That said, it seems some folks really want this to happen, weird as it
> may be. I'm not sure if all these cases are because of wrong designs. A
> possible extension to the mutex interface might be something like this:
> 
>   mutex_pass_owner(struct task_struct *task);
> 
> which would be an atomic unlock/lock pair where the current task
> releases the resource and the indicated task gains it. However it must
> be understood that from the POV of 'current' this should be treated as
> an unlock action.

This won't help if I want to release from an interrupt handler or tasklet.

	Regards
		Oliver
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