linux-kernel - Re: drivers/firmware/google/vpd.c: duplicate sysfs file

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Message-ID: <CABXOdTc-4dcuOvfQCUVB-JUcjK-Tc6xi7THAfLJjP1cJQFn8sQ@mail.gmail.com>
Date:   Mon, 13 Nov 2017 12:14:41 -0800
From:   Guenter Roeck <groeck@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>,
        Wei-Ning Huang <wnhuang@...gle.com>
Subject: Re: drivers/firmware/google/vpd.c: duplicate sysfs file

The sysfs warning, yes. However, after unbinding and rebinding the
driver, "cat /sys/firmware/vpd/rw_raw" will result in a crash.

Sequence:

echo vpd > /sys/bus/platform/drivers/vpd/unbind
echo vpd > /sys/bus/platform/drivers/vpd/bind # <-- nasty message

cat /sys/firmware/vpd/rw_raw # <-- crash

Guenter

On Mon, Nov 13, 2017 at 11:23 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Mon, Nov 13, 2017 at 11:09:21AM -0800, Guenter Roeck wrote:
>> On Mon, Nov 13, 2017 at 11:04 AM, Dmitry Torokhov
>> <dmitry.torokhov@...il.com> wrote:
>> >
>> > On Mon, Nov 13, 2017 at 10:18:35AM -0800, Randy Dunlap wrote:
>> > > On 11/13/2017 06:41 AM, Guenter Roeck wrote:
>> > > >
>> > > >
>> > > > On Sun, Nov 12, 2017 at 10:36 PM, Randy Dunlap <rdunlap@...radead.org <mailto:rdunlap@...radead.org>> wrote:
>> > > >
>> > > >     sysfs: cannot create duplicate filename '/devices/platform/vpd'
>> > > >
>> > > >     on the second load of this driver.  I.e.,
>> > > >
>> > > >     modprobe vpd-sysfs
>> > > >     rmmod vpd-sysfs
>> > > >     modprobe vpd-sysfs
>> > > >     [boom]
>> > > >
>> > > > Neither the platform device nor the platform driver driver are ever unregistered, so this isn't entirely surprising. I'll try to reproduce and send a patch.
>> > >
>> > >
>> > > Seems to be a common theme:
>> > >
>> > > google> grep --color=never "platform.*register" *.c
>> > > coreboot_table-acpi.c:        return platform_driver_register(&coreboot_table_acpi_driver);
>> > > coreboot_table-of.c:  return platform_driver_register(&coreboot_table_of_driver);
>> >
>> > These are not unloadable (for better or worse) - they do not have
>> > module_exit() in them.
>> >
>> > >
>> > > gsmi.c:       gsmi_dev.pdev = platform_device_register_full(&gsmi_dev_info);
>> > > gsmi.c:       platform_device_unregister(gsmi_dev.pdev);
>> > > gsmi.c:       platform_device_unregister(gsmi_dev.pdev);
>> > > [looks good]
>> > >
>> > > memconsole-coreboot.c:        pdev = platform_device_register_simple("memconsole", -1, NULL, 0);
>> > > memconsole-coreboot.c:        platform_driver_register(&memconsole_driver);
>> >
>> > Same here: not unloadable.
>> >
>> > >
>> > > vpd.c:        pdev = platform_device_register_simple("vpd", -1, NULL, 0);
>> > > vpd.c:        platform_driver_register(&vpd_driver);
>> >
>> > Arguably this should not even be a platform driver, there is no hardware
>> > behind it. I was planning on purring some notifiers into coreboot table
>> > driver and using notifiers to attach vpd to them. -ENOTIME though.
>> >
>> Two options for now: clean it up and make it unloadable, or make it bool
>> and drop the exit function. Any preference ?
>>
>> The problem is easy to reproduce even with the driver is built into
>> the kernel with a simple unbind/bind sequence. And after the unbind,
>> it is easy to crash the system since the sysfs attributes are still there.
>
> The kernel should not 'crash', just spit out a nasty warning, right?
>
> thanks,
>
> greg k-h