linux-kernel - Re: [RFC PATCH 3/3] dma-mapping: clear dma

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Message-ID: <20180914155706.GA906@kunai>
Date:   Fri, 14 Sep 2018 17:57:06 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        iommu@...ts.linux-foundation.org, Christoph Hellwig <hch@....de>,
        linux-renesas-soc@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] dma-mapping: clear dma_parms on teardown, too

On Fri, Sep 14, 2018 at 02:23:51PM +0100, Robin Murphy wrote:
> On 13/09/18 16:17, Wolfram Sang wrote:
> > While sanitizig the pointer for dma_ops on teardown, do the same for
> > dma_parms, too. Rename the function to have a more generic name.
> 
> Upon closer inspection, it looks like there are some cases (at least PCI and
> MFD) where dma_parms is installed by the parent/bus at device creation, and
> therefore remains valid and *would* be expected to persist across the child
> device's driver unbinding and rebinding - seems this is more complex than I
> first thought, sorry.

No problem. I am thankful I understand more details. So, the life cycle
of dma_parms is truly that of the device. Which means that the drivers
using devm_kzalloc in their probe, should ideally clear the pointer on
unbind. Otherwise, it is not possible to say if the non-NULL dma_parms
is intended or dangling. Which makes my initial dmam_set_dma_parms()
approach look not too bad, I'd think?

However, I don't want to push hard with this one. If you think this is
too academic, I'll just leave it for now...


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