Re: [PATCH v2 04/11] drivers/base/devcoredump: convert devcd_count to counter_atomic32

[Shuah Khan]

On 10/7/20 12:15 PM, Kees Cook wrote:
> On Tue, Oct 06, 2020 at 02:44:35PM -0600, Shuah Khan wrote:
> > counter_atomic* is introduced to be used when a variable is used as
> > a simple counter and doesn't guard object lifetimes. This clearly
> > differentiates atomic_t usages that guard object lifetimes.
> >
> > counter_atomic* variables will wrap around to 0 when it overflows and
> > should not be used to guard resource lifetimes, device usage and
> > open counts that control state changes, and pm states.
> >
> > devcd_count is used to track dev_coredumpm device count and used in
> > device name string. It doesn't guard object lifetimes, device usage
> > counts, device open counts, and pm states. There is very little chance
> > of this counter overflowing. Convert it to use counter_atomic32.
> >
> > This conversion doesn't change the overflow wrap around behavior.
> >
> > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
>
> I actually wonder if this should use refcount_t just because it is
> designed to be an alway-unique value. It is hard to imagine ever causing
> this to overflow, but why not let it be protected?

This is one of the cases where devcd_count doesn't guard lifetimes,
however if it ever overflows, refcount_t is a better choice.

If we decide refcount_t is a better choice, I can drop this patch
and send refcount_t conversion patch instead.

Greg! Any thoughts on refcount_t for this being a better choice?


thanks,
-- Shuah