linux-kernel - Re: [PATCH v3 1/1] ACPI: scan: Use unique number for instance

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Date:   Mon, 22 Mar 2021 17:02:33 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "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 v3 1/1] ACPI: scan: Use unique number for instance_no

On Mon, Mar 22, 2021 at 4:57 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Fri, Mar 19, 2021 at 8:21 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > 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.
> >
> > Replace above mentioned approach by using IDA framework.

...

> > +       result = ida_simple_get(&acpi_device_bus_id->instance_ida, 0, 255, GFP_KERNEL);
>
> This is ida_alloc_range(ida, start, (end) - 1, gfp), so I think it
> should be 256 above, instead of 255.

Ah, good catch!


> While at it, though, there can be more than 256 CPU devices easily on
> contemporary systems, so I would use a greater number here.  Maybe
> 4096 and define a symbol for it?

I was thinking about it, but there is a problem with the device name,
since it will break a lot of code,
And taking into account that currently we don't change the behaviour
it is good enough per se as a fix.

That said, we may extend by an additional patch with a logic like this:

res = ida_get(4096)
if (res < 0)
  return res;
if (res >= 256)
 use %04x
else
 use %02x

Would it make sense to you?


-- 
With Best Regards,
Andy Shevchenko