Date: Wed, 23 Jul 2014 17:10:40 +0200
From: Joerg Roedel <joro@8bytes.org>
To: Greg Edwards <gedwards@ddn.com>
Cc: David Woodhouse <dwmw2@infradead.org>, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu/vt-d: fix race between free_irte() and get_irte()
Message-ID: <20140723151040.GB14017@8bytes.org>
References: <20140722142719.GA28143@psuche.datadirectnet.com>
 <20140723144024.GA14017@8bytes.org>
 <20140723144917.GA26986@psuche.datadirectnet.com>
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On Wed, Jul 23, 2014 at 08:49:17AM -0600, Greg Edwards wrote:
> On Wed, Jul 23, 2014 at 04:40:24PM +0200, Joerg Roedel wrote:
> > On Tue, Jul 22, 2014 at 08:27:19AM -0600, Greg Edwards wrote:
> >> get_irte() can race with free_irte() and dereference a NULL iommu
> >> pointer.
> >
> > Have you seen any real occurance of this race? Get_irte is called in the
> > set_affinity path, how can that race with the irq being freed?
> 
> Yes, that's how we hit it.  A process was setting the CPU affinity while
> QEMU was releasing the IRQ.  We have a CI stress test that turned this
> up.

Can you update the commit message with the details of how this race can
be triggered, ideally with a stack-trace of a real crash you triggered
because of this issue?


Thanks,

	Joerg

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