linux-kernel - Re: [PATCH] x86: irq: Check for valid irq descriptor in check_irq_vectors_for_cpu

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Date:	Fri, 6 Feb 2015 13:28:02 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Joerg Roedel <jroedel@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, alnovak@...e.com
Subject: Re: [PATCH] x86: irq: Check for valid irq descriptor in
 check_irq_vectors_for_cpu_disable

Hi Jiang,

On Thu, Feb 05, 2015 at 01:51:26PM +0800, Jiang Liu wrote:
> Reviewed-by: Jiang Liu <jiang.liu@...ux.intel.com>

Thanks for your review.

> Actually there's another racing pattern.
> for (irq = 0; irq < nr_irqs; irq++) {
> 	desc = irq_to_desc(irq);
> 	access desc->xxx
> }
> 
> When sparsing IRQ is enabled, there's no mechanism to protect
> desc returned by irq_to_desc(). Once I have considered a brute
> solution of disabling freeing of irq_desc:(

Hmm, how about wrapping the places that use irq_desc in rcu_read_lock()
and do a synchronize_rcu() before we free it (at least in the SPARSE_IRQ
case)? It wouldn't be a real RCU data structure, but we make at least
sure that we don't free an irq_desc thats in use.


	Joerg

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