linux-kernel - Re: [patch] i386/x86_64: smp_call

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Date:	Thu, 07 Jun 2007 20:22:12 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Satyam Sharma <satyam.sharma@...il.com>
CC:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jan Glauber <jan.glauber@...ibm.com>,
	David Miller <davem@...emloft.net>, akpm@...l.org,
	mingo@...e.hu, ak@...e.de, schwidefsky@...ibm.com,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...hat.com>
Subject: Re: [patch] i386/x86_64: smp_call_function locking inconsistency

Satyam Sharma wrote:
>
> Oh wait, the on_one_cpu() patch proposes on UP:
>
> +static inline int on_one_cpu(int cpu, void (*func)(void *info), void
> *info,
> +                 int retry, int wait)
> +{
>
> /* this needs a if (cpu == 0) check here, IMO */
>
> +    local_irq_disable();
> +    func(info);
> +    local_irq_enable();
> +    return 0;
>
> /* else WARN and return -EINVAL; */
>
> +}
>
> which is broken without the suggested additions, IMHO
> (this is what got me into this in the first place). There
> _is_ a difference between on_each_cpu() and the
> smp_call_function* semantics (as discussed on the other
> thread -- gargh! my mistake for opening this discussion up
> on so many threads), and in its current form on_one_cpu()
> has quite confused semantics, trying to mix the two. I guess
> on_one_cpu() would be better off simply being just an
> atomic wrapper over smp_processor_id() and
> smp_call_function_single() (which is the *real* issue that
> needs solving in the first place), and do it well.
>

This is on UP, so (cpu == 0) is trivially true.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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