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Date:   Thu, 31 Mar 2022 09:25:20 +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
Message-ID: <YkVJUBK5uHl7ELdv@atomide.com>
References: <20220216025249.3459465-1-baolu.lu@linux.intel.com>
 <20220216025249.3459465-9-baolu.lu@linux.intel.com>
 <YkRiawC2T9g+CHSJ@atomide.com>
 <20220330142340.GA2111031@nvidia.com>
 <YkSRKZcJO0q3v5WL@atomide.com>
 <20220330173323.GA2120790@nvidia.com>
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Hi,

* Jason Gunthorpe <jgg@nvidia.com> [220330 17:31]:
> On Wed, Mar 30, 2022 at 08:19:37PM +0300, Tony Lindgren wrote:
> 
> > > > __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.
> 
> That makes alot more sense
>  
> > > Can you find the code that is the NULL deref?
> > 
> > I can debug a bit more tomorrow.
> 
> Looks like omap's omap_iommu_probe_device() is buggy, it returns 0 on
> error paths:
> 
> 	num_iommus = of_property_count_elems_of_size(dev->of_node, "iommus",
> 						     sizeof(phandle));
> 	if (num_iommus < 0)
> 		return 0;
> 
> This function needs to return an errno -ENODEV
> 
> Otherwise it causes a NULL dev->iommu->iommu_dev and dev_iommu_ops() will
> crash.

You got it. This fixes the issue for me. Looks like the regression already
happened earlier and recent changes just expose it.

For reference, fix posted at:

https://lore.kernel.org/linux-iommu/20220331062301.24269-1-tony@atomide.com/T/#u

Regards,

Tony