linux-kernel - Re: initialize a mutex into locked state?

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Message-ID: <20160617141912.GS30154@twins.programming.kicks-ass.net>
Date:	Fri, 17 Jun 2016 16:19:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Drokin <green@...uxhacker.ru>
Cc:	Mailing List <linux-kernel@...r.kernel.org>, mingo@...hat.com,
	arjan@...ux.intel.com, "J . Bruce Fields" <bfields@...ldses.org>,
	Jeff Layton <jlayton@...chiereds.net>
Subject: Re: initialize a mutex into locked state?

On Fri, Jun 17, 2016 at 10:14:10AM -0400, Oleg Drokin wrote:
> 
> On Jun 17, 2016, at 4:25 AM, Peter Zijlstra wrote:
> 
> > On Wed, Jun 15, 2016 at 02:23:35PM -0400, Oleg Drokin wrote:
> >> Hello!
> >> 
> >>  To my surprise I found out that it's not possible to initialise a mutex into
> >>  a locked state.
> >>  I discussed it with Arjan and apparently there's no fundamental reason
> >>  not to allow this.
> > 
> > There is. A mutex _must_ have an owner. If you can initialize it in
> > locked state, you could do so statically, ie. outside of the context of
> > a task.
> 
> What's wrong with disallowing only static initializers, but allowing dynamic ones?
> Then there is a clear owner.

At which point, what wrong with the simple:

	mutex_init(&m);
	mutex_lock(&m);

Sequence? Its obvious, has clear semantics and doesn't extend the API.