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Date:	Sun, 27 May 2012 09:41:26 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Dimitri Sivanich <sivanich@....com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Yinghai Lu <yinghai@...nel.org>,
	Naga Chumbalkar <nagananda.chumbalkar@...com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: check for valid irq_cfg pointer in smp_irq_move_cleanup_interrupt

I have realized the same issue with typical usages of for_each_irq_desc(), 
which may access freed memory with SPARSE_IRQ. My naive solution was to
avoid freeing irq_desc even SPARSE_IRQ_ is enabled.

        for_each_irq_desc(i, desc) {
                raw_spin_lock_irq(&desc->lock);

On 05/26/2012 06:18 PM, Thomas Gleixner wrote:
> On Fri, 25 May 2012, Suresh Siddha wrote:
>> On Thu, 2012-05-24 at 21:16 +0200, Thomas Gleixner wrote:
>> There are other (not-so common) irq desc references, like in the
>> show_interrupts() (cat /proc/interrupts path) etc, that does things like
>> this in the process context:
>>
>>         desc = irq_to_desc(i);
>>         if (!desc)
>>                 return 0;
>>
>>         raw_spin_lock_irqsave(&desc->lock, flags);
>>
>> May be we should introduce something like
>> get_irq_desc_locked()/put_irq_desc_locked() that can safely access the
>> irq desc with pre-emption/irq's disabled and lock it etc. And the
>> synchronize_sched() will enable the destroy_irq()/free_desc() to free it
>> safely etc.
> 
> I want to avoid that and instead use proper refcounting. The reason is
> that we want to move the irq descriptor when the affinity changes
> nodes, and for that we need refcounting anyway.
> 
> Thanks,
> 
> 	tglx
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