Re: [PATCH net v3] ptp: prevent possible ABBA deadlock in ptp_clock_freerun()

[Vladimir Oltean]

On Sat, Jul 19, 2025 at 09:40:22PM +0900, Jeongjun Park wrote:
> diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c
> index 7febfdcbde8b..b16c66c254ae 100644
> --- a/drivers/ptp/ptp_vclock.c
> +++ b/drivers/ptp/ptp_vclock.c
> @@ -154,6 +154,20 @@ static long ptp_vclock_refresh(struct ptp_clock_info *ptp)
>  	return PTP_VCLOCK_REFRESH_INTERVAL;
>  }
>  
> +#ifdef CONFIG_LOCKDEP
> +static void ptp_vclock_set_subclass(struct ptp_clock *ptp)
> +{
> +	lockdep_set_subclass(&ptp->n_vclocks_mux, PTP_LOCK_VIRTUAL);
> +	lockdep_set_subclass(&ptp->clock.rwsem, PTP_LOCK_VIRTUAL);
> +	lockdep_set_subclass(&ptp->tsevqs_lock, PTP_LOCK_VIRTUAL);
> +	lockdep_set_subclass(&ptp->pincfg_mux, PTP_LOCK_VIRTUAL);

Every other lock except &ptp->clock.rwsem is unrelated, and I wouldn't
touch what is unrelated as part of a bug fix. That, plus I believe this
breaks the data encapsulation of struct posix_clock. At least CC the
"POSIX CLOCKS and TIMERS" maintainers in v4, so that they're aware of
your intentions.

> +}
> +#else
> +static void ptp_vclock_set_subclass(struct ptp_clock *ptp)
> +{
> +}
> +#endif
> +

lockdep_set_subclass() has shim definitions for CONFIG_LOCKDEP=n, you
don't need the #ifdef.