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Date:   Wed, 30 Mar 2022 20:19:37 +0300
From:   Tony Lindgren <tony@atomide.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Christoph Hellwig <hch@infradead.org>,
        Ben Skeggs <bskeggs@redhat.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Ashok Raj <ashok.raj@intel.com>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Eric Auger <eric.auger@redhat.com>,
        Liu Yi L <yi.l.liu@intel.com>,
        Jacob jun Pan <jacob.jun.pan@intel.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Christoph Hellwig <hch@lst.de>, linux-omap@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, regressions@lists.linux.dev
Subject: Re: [PATCH v4 8/9] iommu: Remove unused argument in
 is_attach_deferred
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 <YkRiawC2T9g+CHSJ@atomide.com>
 <20220330142340.GA2111031@nvidia.com>
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* Jason Gunthorpe <jgg@nvidia.com> [220330 14:21]:
> On Wed, Mar 30, 2022 at 05:00:39PM +0300, Tony Lindgren wrote:
> > Hi,
> > 
> > * Lu Baolu <baolu.lu@linux.intel.com> [700101 02:00]:
> > > The is_attach_deferred iommu_ops callback is a device op. The domain
> > > argument is unnecessary and never used. Remove it to make code clean.
> > 
> > Looks like this causes a regression for at least drivers/iommu/omap-iommu.c.
> > 
> > To me it seems the issue is there is no is_attach_deferred implemented, so
> > we get a NULL pointer dereference at virtual address 00000008:
> > 
> > __iommu_probe_device from probe_iommu_group+0x2c/0x38
> > probe_iommu_group from bus_for_each_dev+0x74/0xbc
> > bus_for_each_dev from bus_iommu_probe+0x34/0x2e8
> > bus_iommu_probe from bus_set_iommu+0x80/0xc8
> > bus_set_iommu from omap_iommu_init+0x88/0xcc
> > omap_iommu_init from do_one_initcall+0x44/0x24c
> > 
> > Any ideas for a fix?
> > 
> > It would be good to fix this quickly so we don't end up with a broken
> > v5.18-rc1..
> > 
> > For reference, this is mainline commit 41bb23e70b50 ("iommu: Remove unused
> > argument in is_attach_deferred").
> 
> Are you confident in the bisection? I don't see how that commit could
> NULL deref..

Oops sorry you're right, the breaking commit is a different patch, it's
3f6634d997db ("iommu: Use right way to retrieve iommu_ops") instead. I must
have picked the wrong commit while testing.

> Can you find the code that is the NULL deref?

I can debug a bit more tomorrow.

Regards,

Tony