On Fri, Mar 19, 2021 at 7:06 PM Andy Shevchenko
[off-list ref] wrote:

On Fri, Mar 19, 2021 at 06:00:38PM +0100, Rafael J. Wysocki wrote:

quoted

On Fri, Mar 12, 2021 at 5:02 PM Andy Shevchenko
[off-list ref] wrote:

quoted

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."