linux-kernel - Re: [PATCH 1/10] Add generic helpers for arch IPI function calls

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Date:	Wed, 30 Apr 2008 15:56:47 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	npiggin@...e.de, linux-arch@...r.kernel.org, mingo@...e.hu,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/10] Add generic helpers for arch IPI function calls

Jens Axboe wrote:
> +/*
> + * smp_call_function_single - Run a function on a specific CPU
> + * @func: The function to run. This must be fast and non-blocking.
> + * @info: An arbitrary pointer to pass to the function.
> + * @retry: Unused
>   

I wonder if it isn't finally time to drop this parameter?  Now that 
there aren't a zillion arch implementations of this to fix, we only need 
to fix a dozen or so callers.

> + * @wait: If true, wait until function has completed on other CPUs.
> + *
> + * Returns 0 on success, else a negative status code.
> + */
> [...]
> +/**
> + * smp_call_function_mask(): Run a function on a set of other CPUs.
> + * @mask: The set of cpus to run on.
> + * @func: The function to run. This must be fast and non-blocking.
> + * @info: An arbitrary pointer to pass to the function.
> + * @wait: If true, wait (atomically) until function has completed on other CPUs.
> + *
> + * Returns 0 on success, else a negative status code.
> + *
> + * If @wait is true, then returns once @func has returned.
> + *
> + * You must not call this function with disabled interrupts or from a
> + * hardware interrupt handler or from a bottom half handler.
>   

Mention preemption needs to be disabled?  Or allow preemption and take 
appropriate precautions internally?  It's not obvious to me that all the 
callers are calling with preemption disabled.

> + */
> +int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
> +			   int wait)
> +{
> +	struct call_function_data *data;
> +	cpumask_t allbutself;
> +	unsigned long flags;
> +	int cpu, num_cpus;
> +
> +	/* Can deadlock when called with interrupts disabled */
> +	WARN_ON(wait && irqs_disabled());
>   
WARN_ON(preemptible())?
preempt_disable()?

> +
> +	cpu = smp_processor_id();
> +	allbutself = cpu_online_map;
> +	cpu_clear(cpu, allbutself);
> +	cpus_and(mask, mask, allbutself);
> +	num_cpus = cpus_weight(mask);
>   
    J
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