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

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Date:   Fri, 19 Mar 2021 18:00:38 +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>,
        "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 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().

Yes, there is one, the instance_no decrementation is clearly incorrect.

> Replace plain integer approach by using IDA framework.

Also the general idea of using IDA for the instance numbering is a good one IMO.

> Fixes: e49bd2dd5a50 ("ACPI: use PNPID:instance_no as bus_id of ACPI device")
> Fixes: ca9dc8d42b30 ("ACPI / scan: Fix acpi_bus_id_list bookkeeping")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/acpi/internal.h |  4 ++-
>  drivers/acpi/scan.c     | 55 +++++++++++++++++++++++++++++++++++++----
>  2 files changed, 53 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
> index e6a5d997241c..6fee4f71ba1c 100644
> --- a/drivers/acpi/internal.h
> +++ b/drivers/acpi/internal.h
> @@ -9,6 +9,8 @@
>  #ifndef _ACPI_INTERNAL_H_
>  #define _ACPI_INTERNAL_H_
>
> +#include <linux/idr.h>
> +
>  #define PREFIX "ACPI: "
>
>  int early_acpi_osi_init(void);
> @@ -98,7 +100,7 @@ extern struct list_head acpi_bus_id_list;
>
>  struct acpi_device_bus_id {
>         const char *bus_id;
> -       unsigned int instance_no;
> +       struct ida no;

struct ida instance_ida; ?

>         struct list_head node;
>  };
>
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index a184529d8fa4..a118a58f7dad 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -468,9 +468,27 @@ static void acpi_device_release(struct device *dev)
>         kfree(acpi_dev);
>  }
>
> +static int acpi_device_get_instance_no(struct acpi_device *device)
> +{
> +       const char *p;
> +       int result;
> +       int error;
> +
> +       p = strrchr(dev_name(&device->dev), ':');
> +       if (!p)
> +               return -ENODATA;
> +
> +       error = kstrtoint(p + 1, 16, &result);
> +       if (error)
> +               return error;
> +
> +       return result;
> +}

I don't like the above at all.

I would just store the instance number in struct acpi_device_pnp (say).