linux-kernel - Re: [PATCH v9 03/16] iommu/exynos: fix page table maintenance

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Message-ID: <20130814104938.GF4491@8bytes.org>
Date:	Wed, 14 Aug 2013 12:49:38 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Grant Grundler <grundler@...omium.org>
Cc:	Tomasz Figa <t.figa@...sung.com>,
	Cho KyongHo <pullip.cho@...sung.com>,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
	devicetree@...r.kernel.org, Kukjin Kim <kgene.kim@...sung.com>,
	Prathyush <prathyush.k@...sung.com>,
	Rahul Sharma <rahul.sharma@...sung.com>,
	Subash Patel <supash.ramaswamy@...aro.org>,
	Antonios Motakis <a.motakis@...tualopensystems.com>,
	kvmarm@...ts.cs.columbia.edu,
	Sachin Kamat <sachin.kamat@...aro.org>
Subject: Re: [PATCH v9 03/16] iommu/exynos: fix page table maintenance

On Thu, Aug 08, 2013 at 11:28:44AM -0700, Grant Grundler wrote:
> I can't speak to the previous BUG_ON(). I believe the EADDRESSINUSE
> failures could be either WARN_ON or BUG_ON.   This condition is
> clearly a bug in the generic IOMMU allocator and I think that's why
> KyongHo Cho used BUG_ON.
> 
> Handing out duplicate addresses will generally lead to some sort of
> data corruption or other fault depending on how robust the underlying
> device drivers are written.  So my preference is a BUG_ON to
> immediately flag this condition instead of hoping a device driver will
> correctly handling the dma mapping failure (Some do, most currently
> don't).
> 
> WARN_ON() + return -EADDRESSINUSE would be a good alternative.

Even if it is a real BUG condition, I don't think it is worth to stop
execution at this point. It makes debugging harder and the system less
reliable. I prefer to go with the WARN_ON and an error return value.


	Joerg


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