From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Saravana Kannan <saravanak@google.com>,
Mark Brown <broonie@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Guenter Roeck <linux@roeck-us.net>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Android Kernel Team <kernel-team@android.com>,
linux-spi <linux-spi@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] spi: Fix spi device unregister flow
Date: Mon, 3 May 2021 13:16:48 +0300 [thread overview]
Message-ID: <CAHp75VfFigeSDVixOZTy7feQh2-V+zzKPNpNFViPGg6MoZ3t6A@mail.gmail.com> (raw)
In-Reply-To: <20210503100733.GA8114@wunner.de>
On Mon, May 3, 2021 at 1:07 PM Lukas Wunner <lukas@wunner.de> wrote:
> On Mon, Apr 26, 2021 at 04:56:38PM -0700, Saravana Kannan wrote:
> > When an SPI device is unregistered, the spi->controller->cleanup() is
> > called in the device's release callback. That's wrong for a couple of
> > reasons:
> >
> > 1. spi_dev_put() can be called before spi_add_device() is called. And
> > it's spi_add_device() that calls spi_setup(). This will cause clean()
> > to get called without the spi device ever being setup.
>
> Well, yes, but it's not a big problem in practice so far:
>
> I've checked all drivers and there are only four which are affected
> by this: spi-mpc512x-psc.c spi-pic32.c spi-s3c64xx.c spi-st-ssc4.c
>
> They all fiddle with the chipselect GPIO in their ->cleanup hook
> and the GPIO may not have been requested yet because that happens
> during ->setup.
>
> All the other drivers merely invoke kzalloc() on ->setup and kfree()
> on ->cleanup. The order doesn't matter in this case because
> kfree(NULL) is a no-op.
Thanks, Lukas, for jumping in.
> > 2. There's no guarantee that the controller's driver would be present by
> > the time the spi device's release function gets called.
>
> How so? spi_devices are instantiated on ->probe of the controller
> via spi_register_controller() and destroyed on ->remove via
> spi_unregister_controller(). I don't see how the controller driver
> could ever be unavailable, so this point seems moot.
>
>
> > Fix these issues by simply moving the cleanup from the device release
> > callback to the actual spi_unregister_device() function.
>
> Unfortunately the fix is wrong, it introduces a new problem:
>
> > @@ -713,6 +717,8 @@ void spi_unregister_device(struct spi_device *spi)
> > if (!spi)
> > return;
> >
> > + spi_cleanup(spi);
> > +
> > if (spi->dev.of_node) {
> > of_node_clear_flag(spi->dev.of_node, OF_POPULATED);
> > of_node_put(spi->dev.of_node);
>
> Now you're running ->cleanup before the SPI slave's driver is unbound.
> That's bad, the driver may need to access the physical device on unbound,
> e.g. to quiesce interrupts. That may not work now because the
> slave's controller_state is gone.
>
> NAK, this needs to be reverted.
I guess somebody should send the actual revert. Are you going to do so?
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2021-05-03 10:17 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-26 23:56 [PATCH] spi: Fix spi device unregister flow Saravana Kannan
2021-04-27 6:52 ` Andy Shevchenko
2021-04-27 10:48 ` Mark Brown
2021-04-27 11:42 ` Andy Shevchenko
2021-04-27 11:49 ` Greg Kroah-Hartman
2021-04-27 15:02 ` Saravana Kannan
2021-04-28 16:53 ` Mark Brown
2021-05-03 10:07 ` Lukas Wunner
2021-05-03 10:16 ` Andy Shevchenko [this message]
2021-05-03 17:21 ` Saravana Kannan
2021-05-03 17:56 ` Lukas Wunner
2021-05-03 18:15 ` Saravana Kannan
2021-05-04 9:17 ` Lukas Wunner
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