linux-kernel - Re: spin_is_locked() broken for uniprocessor?

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Message-ID: <20090819115301.563be6da@lxorguk.ukuu.org.uk>
Date:	Wed, 19 Aug 2009 11:53:01 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Howells <dhowells@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, dhowells@...hat.com,
	Kumar Gala <galak@...nel.crashing.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux-Kernel List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linuxppc-dev list <linuxppc-dev@...abs.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: spin_is_locked() broken for uniprocessor?

On Wed, 19 Aug 2009 10:38:06 +0100
David Howells <dhowells@...hat.com> wrote:

> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > > which implies to me that spin_is_locked() will always return false.  Is this
> > > expected behavior.
> > 
> > That's wrong. spin_is_locked should always return true on UP.
> 
> Surely it's not that simple?  Maybe spin_is_lock() should be undefined on UP.

That would lead to a lot of

#ifdef CONFIG_SMP

#endif

in drivers because there is driver code that uses spin_is_locked() in
fairly sensible fashion when dealing with locking.
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