linux-kernel - Re: [PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of

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Date:   Fri, 30 Oct 2020 09:27:23 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, <joro@...tes.org>,
        <heiko@...ech.de>, <jeffy.chen@...k-chips.com>
CC:     <iommu@...ts.linux-foundation.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-rockchip@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>
Subject: Re: [PATCH] iommu/rockchip: check return value of
 of_find_device_by_node() in rk_iommu_of_xlate()


On 2020/10/29 21:51, Robin Murphy wrote:
> On 2020-10-29 13:19, yukuai (C) wrote:
>>
>> On 2020/10/29 18:08, Robin Murphy wrote:
>>> On 2020-10-29 09:22, Yu Kuai wrote:
>>>> If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
>>>> dereference will be triggered. Thus return error code if
>>>> of_find_device_by_node() failed.
>>>
>>> How can that happen? (Given that ".suppress_bind_attrs = true")
>>>
>>> Robin.
>>
>> I'm not sure if that could happen...
>>
>> My thought is that it's better to do such checking to aviod any possible
>> problem.
> 
> ->of_xlate() is only invoked on the specific set of ops returned by 
> iommu_ops_from_fwnode(). In turn, iommu_ops_from_fwnode() will only 
> return those ops if the driver has successfully probed and called 
> iommu_register_device() with the relevant DT node. For the driver to 
> have been able to probe at all, a platform device associated with that 
> DT node must have been created, and therefore of_find_device_by_node() 
> cannot fail.
> 
> If there ever were some problem serious enough to break that fundamental 
> assumption, then I *want* these drivers to crash right here, with a nice 
> clear stack trace to start debugging from. So no, I firmly disagree that 
> adding redundant code, which will never do anything except attempt to 
> paper over catastrophic memory corruption, is "better". Sorry :)
> 

Sounds reasonable, thanks for your explanation

Yu Kuai