linux-kernel - Re: [PATCH 5/7] iommu/arm-smmu-v3: Allow building as a module

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Message-ID: <20191105121508.GA3479@8bytes.org>
Date:   Tue, 5 Nov 2019 13:15:08 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Will Deacon <will@...nel.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Robin Murphy <robin.murphy@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH 5/7] iommu/arm-smmu-v3: Allow building as a module

Hi Will,

On Thu, Oct 31, 2019 at 03:42:47PM +0000, Will Deacon wrote:
> Generally, I think unloading the IOMMU driver module while there are
> active users is a pretty bad idea, much like unbinding the driver via
> /sys in the same situation would also be fairly daft. However, I *think*
> the code in __device_release_driver() tries to deal with this by
> iterating over the active consumers and ->remove()ing them first.
> 
> I'm without hardware access at the moment, so I haven't been able to
> test this myself. We could nobble the module_exit() hook, but there's
> still the "force unload" option depending on the .config.

Okay, but besides the force-unload case, can we prevent accidential
unloading by taking a reference to the module in add_device() and release
it in remove_device()?

Regards,

	Joerg