# Re: \[PATCH 14/15\] kernel: convert futex\_pi\_state.refcount from atomic\_t to refcount\_t

- From: Peter Zijlstra \<peterz@infradead.org\>
- Date: 2017-07-07 09:26:21 
- List: cgroups
- Page: https://ratatoskr.run/cgroups/2017/07/124158
- Thread: https://ratatoskr.run/cgroups/2017/07/124139/t.md

```text
On Fri, Jul 07, 2017 at 12:04:28PM +0300, Elena Reshetova wrote:
> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.
> 
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Hans Liljestrand <redacted>
> Signed-off-by: Kees Cook <redacted>
> Signed-off-by: David Windsor <redacted>

I'll let tglx comment on the SoB chain, I know he likes those :-) You
did Cc him right, seeing how he's the maintainer of this stuff..

*sigh* you didn't :-( After so many patches send you _really_ should
know to Cc the right people.

> ---
>  kernel/futex.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)

> @@ -814,7 +815,7 @@ static struct futex_pi_state *alloc_pi_state(void)
>  
>  static void get_pi_state(struct futex_pi_state *pi_state)
>  {
> -	WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
> +	WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
>  }

I think we have refcount_inc() for just that case, no?


```