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Date: Thu, 10 Apr 2008 17:04:19 +0900
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Subject: Re: [patch 11/17] Implement immediate update via stop_machine_run
Cc: kosaki.motohiro@jp.fujitsu.com, akpm@linux-foundation.org,
       Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Andi Kleen <andi@firstfloor.org>, Rusty Russell <rusty@rustcorp.com.au>,
       Jason Baron <jbaron@redhat.com>, Adrian Bunk <bunk@stusta.de>,
       Alexey Dobriyan <adobriyan@gmail.com>,
       Christoph Hellwig <hch@infradead.org>, akpm@osdl.org
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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;
> +}
> +