linux-kernel - Re: [PATCH v1 1/1] ACPI: scan: Use unique number for instance

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Message-ID: <CAJZ5v0hFsfX7A0t4Snr7qsivzmCecSkNxMm6OFaB30PjXspAmQ@mail.gmail.com>
Date:   Fri, 19 Mar 2021 19:44:11 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v1 1/1] ACPI: scan: Use unique number for instance_no

On Fri, Mar 19, 2021 at 7:06 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Fri, Mar 19, 2021 at 06:00:38PM +0100, Rafael J. Wysocki wrote:
> > On Fri, Mar 12, 2021 at 5:02 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > >
> > > Current mechanism of incrementing and decrementing plain integer
> > > to get a next free instance_no when creating an ACPI device is fragile.
> > >
> > > In case of hot plug event or namespace removal of the device instances
> > > with the low numbers the plain integer counter can't cover the gaps
> > > and become desynchronized with real state of affairs. If during next
> > > hot plug event or namespace injection the new instances of
> > > the devices need to be instantiated, the counter may mistakenly point
> > > to the existing instance_no and kernel will complain:
> > > "sysfs: cannot create duplicate filename '/bus/acpi/devices/XXXX1234:02'"
> >
> > This is a slightly convoluted way of stating that there is a bug in
> > acpi_device_del().
>
> Any suggestion how to massage the above?

Why don't you simply say something like "The decrementation of
acpi_device_bus_id->instance_no in acpi_device_del() is incorrect,
because it may cause a duplicate instance number to be allocated next
time a device with the same acpi_device_bus_id is added."