linux-kernel - Re: [PATCH] spi: bcm2835: do not unregister controller in shutdown handler

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Message-ID: <20211004183746.GC3544071@ziepe.ca>
Date:   Mon, 4 Oct 2021 15:37:46 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     Mark Brown <broonie@...nel.org>, f.fainelli@...il.com,
        rjui@...adcom.com, sbranden@...adcom.com,
        bcm-kernel-feedback-list@...adcom.com, nsaenz@...nel.org,
        linux-spi@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        p.rosenberger@...bus.com, linux-integrity@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] spi: bcm2835: do not unregister controller in shutdown
 handler

On Mon, Oct 04, 2021 at 08:30:52PM +0200, Lino Sanfilippo wrote:
> On 04.10.21 at 17:44, Jason Gunthorpe wrote:
> 
> >
> > Well, that is up to the driver implementing this. It looks like device
> > shutdown is called before the userspace is all nuked so yes,
> > concurrency with userspace is a possible concern here.
> >
> 
> So the TPM driver has to handle remove() after shutdown() anyway, right?
> Because even if not caused by the BCM2835 drivers controller unregistration
> something else could unload the module and the problem (NULL pointer access)
> would be the same.

Technically yes, remove shouldn't crash in this ordering - but it
should be difficult for remove to be called after shutdown in any
normal system.

Jason