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Date:   Wed, 30 Mar 2022 11:23:40 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Tony Lindgren <tony@atomide.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
Message-ID: <20220330142340.GA2111031@nvidia.com>
References: <20220216025249.3459465-1-baolu.lu@linux.intel.com>
 <20220216025249.3459465-9-baolu.lu@linux.intel.com>
 <YkRiawC2T9g+CHSJ@atomide.com>
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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..

Can you find the code that is the NULL deref?

Jason