linux-kernel - Re: [patch 11/17] Implement immediate update via stop_machine

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Message-Id: <20080410164159.2327.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Thu, 10 Apr 2008 17:04:19 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	kosaki.motohiro@...fujitsu.com, akpm@...ux-foundation.org,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jason Baron <jbaron@...hat.com>, Adrian Bunk <bunk@...sta.de>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Christoph Hellwig <hch@...radead.org>, akpm@...l.org
Subject: Re: [patch 11/17] Implement immediate update via stop_machine_run

Hi

> -Updating immediate values, cannot rely on smp_call_function() b/c synchronizing
>  cpus using IPIs leads to deadlocks. Process A held a read lock on 
>  tasklist_lock, then process B called apply_imv_update(). Process A received the 
>  IPI and begins executing ipi_busy_loop(). Then process C takes a write lock 
>  irq on the task list lock, before receiving the IPI. Thus, process A holds up 
>  process C, and C can't get an IPI b/c interrupts are disabled. Solve this 
>  problem by using a new 'ALL_CPUS' parameter to stop_machine_run(). Which 
>  runs a function on all cpus after they are busy looping and have disabled 
>  irqs. Since this is done in a new process context, we don't have to worry 
>  about interrupted spin_locks. Also, less lines of code. Has survived 24 hours+
>  of testing...

it seems this patch is must, Why do you separate patch [10/17] and [11/17]?
this patch remove almost portion of [10/17].
IMHO these patch merge into 1 patch is better.


> +static int stop_machine_imv_update(void *imv_ptr)
> +{
> +	struct __imv *imv = imv_ptr;
> +
> +	if (!wrote_text) {

it seems racy.
Why don't need test_and_set?

I think your stop_machine_run(ALL_CPUS) call fn concurrency...


> +		text_poke((void *)imv->imv, (void *)imv->var, imv->size);
> +		wrote_text = 1;
> +		smp_wmb(); /* make sure other cpus see that this has run */
> +	} else
> +		sync_core();
> +
> +	flush_icache_range(imv->imv, imv->imv + imv->size);
> +
> +	return 0;
> +}
> +


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