linux-kernel - Re: [PATCH] iommu/ipmmu-vmsa: Fix crash on early domain free

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Date:   Wed, 7 Nov 2018 16:17:09 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/ipmmu-vmsa: Fix crash on early domain free

On 2018-11-07 4:03 pm, Joerg Roedel wrote:
> On Wed, Nov 07, 2018 at 04:50:40PM +0100, Geert Uytterhoeven wrote:
>> It only got triggered by the combination of commits 6c2fb2ea76361da9
>> ("of/device: Set bus DMA mask as appropriate") and b4ebe6063204da58
>> ("dma-direct: implement complete bus_dma_mask handling"), which is being
>> fixed by "of/device: Really only set bus DMA mask when
>> appropriate" (https://patchwork.kernel.org/patch/10670177/).
> 
> Okay, but the bug is triggered since 6c2fb2ea76361da9, so I took this
> one for the fixes-tag.

FWIW it looks like it *has* always been possible to hit this crash by 
allocating a domain and freeing it again without attaching any devices, 
it's just highly improbable for any sane code to do that explicitly, so 
the real latent triggers are failure paths in external callers (which in 
this case are themselves only being reached thanks to my bug elsewhere).

Robin.