Re: [RFC PATCH 01/11] counters: Introduce counter and counter_atomic

Greg KH
2020-09-23T10:35:00Z

On Tue, Sep 22, 2020 at 07:43:30PM -0600, Shuah Khan wrote:
> Introduce Simple atomic and non-atomic counters.
>
> There are a number of atomic_t usages in the kernel where atomic_t api
> is used strictly for counting and not for managing object lifetime. In
> some cases, atomic_t might not even be needed.
>
> The purpose of these counters is twofold: 1. clearly differentiate
> atomic_t counters from atomic_t usages that guard object lifetimes,
> hence prone to overflow and underflow errors. It allows tools that scan
> for underflow and overflow on atomic_t usages to detect overflow and
> underflows to scan just the cases that are prone to errors. 2. provides
> non-atomic counters for cases where atomic isn't necessary.
>
> Simple atomic and non-atomic counters api provides interfaces for simple
> atomic and non-atomic counters that just count, and don't guard resource
> lifetimes. Counters 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.
>
> Using counter_atomic to guard lifetimes could lead to use-after free
> when it overflows and undefined behavior when used to manage state
> changes and device usage/open states.
>
> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
> ---
> Documentation/core-api/counters.rst | 158 +++++++++++++
> MAINTAINERS | 7 +
> include/linux/counters.h | 343 ++++++++++++++++++++++++++++
> lib/Kconfig | 10 +
> lib/Makefile | 1 +
> lib/test_counters.c | 283 +++++++++++++++++++++++

Tests for new apis, nice!

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>