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Subject: Re: [patch] spinlocks: remove 'volatile'
From: Arjan van de Ven <arjan@infradead.org>
To: "linux-os (Dick Johnson)" <linux-os@analogic.com>
Cc: Ingo Molnar <mingo@elte.hu>, Linus Torvalds <torvalds@osdl.org>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
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Date: Thu, 06 Jul 2006 14:01:07 +0200
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On Thu, 2006-07-06 at 07:59 -0400, linux-os (Dick Johnson) wrote:
> On Thu, 6 Jul 2006, Ingo Molnar wrote:
> 
> >
> > * Linus Torvalds <torvalds@osdl.org> wrote:
> >
> >> I wonder if we should remove the "volatile". There really isn't
> >> anything _good_ that gcc can do with it, but we've seen gcc code
> >> generation do stupid things before just because "volatile" seems to
> >> just disable even proper normal working.
> 
> Then GCC must be fixed. The keyword volatile is correct. It should
> force the compiler to read the variable every time it's used.

this is not really what the C standard says.



> This is not pointless. If GCC generates bad code, tell the
> GCC people. The volatile keyword is essential.

no the "volatile" semantics are vague, trecherous and evil. It's a LOT
better to insert the well defined "barrier()" in the right places.