linux-kernel - Re: [PATCH] check spinlock_t/rwlock_t argument type on non-SMP builds

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Date:	Sat, 18 Jul 2009 14:14:13 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave <kilroyd@...glemail.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] check spinlock_t/rwlock_t argument type on non-SMP
	builds


* Dave <kilroyd@...glemail.com> wrote:

> Ingo Molnar wrote:
> > * David Kilroy <kilroyd@...glemail.com> wrote:
> > 
> >> When writing code for UP without CONFIG_DEBUG_SPINLOCK it's easy 
> >> to get the first argument to the spinlock/rwlock functions wrong. 
> >> This is because the parameter is not actually used in this 
> >> configuration.
> >>
> >> Typically you will only find out it's wrong
> >>  * by rebuilding with CONFIG_SMP or CONFIG_DEBUG_SPINLOCK
> >>  * after you've submitted your beautiful patch series.
> >>
> >> The first means a long wait, and the latter is a bit late.
> >>
> >> Add typechecking on the first argument of these macro functions. 
> >> Note that since the typecheck now references the variable, the 
> >> explicit read is redundant and can be removed.
> >>
> >> This change causes compiler warnings in net/ipv4/route.c, as this 
> >> passes NULL as the first argument in the UP configuration. Simply 
> >> cast this.
> > 
> > Wondering - can the wrappers be moved from CPP land to C land by 
> > turning them into inlines? (i havent checked all usages so there 
> > might be some surprises, but by and large it ought to be 
> > possible.)
> 
> I thought about doing it that way. I decided not to because I 
> suspected it would be harder to verify that the behaviour is 
> unchanged.

These things break noisily if they are wrong so i wouldnt be worried 
about that aspect.

> Also the _lock_irqsave functions output to the flags parameter 
> (which isn't a pointer) so that has to remain a macro.

Do we still need it? I remember it was originally due to some 
sparc32-ness, but meanwhile that's fixed in Sparc so we can 
generally pass irq flags around at will.

> If you'd really rather an inline version, I can spend some time 
> looking into it.

Would be nice.

	Ingo
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