linux-kernel - Re: [PATCH v2 1/1] ACPI: scan: Use unique number for instance

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Message-ID: <CAJZ5v0jihmos4gza_+0MzGsUfxJJ-5LGBOURVebdGsE_RuPhFA@mail.gmail.com>
Date:   Fri, 19 Mar 2021 19:51:00 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "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>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>
Subject: Re: [PATCH v2 1/1] ACPI: scan: Use unique number for instance_no

On Fri, Mar 19, 2021 at 7:33 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 buggy.
>
> The simple integer and operations line increment and decrement
> on top of it can't cover the possible gaps during run time. The
> arbitrary instantiation and elimination of the devices is racy

But it isn't racy AFAICS.  It always happens under acpi_device_lock().

> and after a couple of iterations with unequal amount of devices
> being added and removed we may reproduce a bug: