On Fri, Mar 12, 2021 at 5:02 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> ---
> 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).
