Re: [PATCH net] net/sched: taprio: fix duration_to_length()

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Thu, May 23, 2024 at 01:45:49PM +0000, Eric Dumazet wrote:
> duration_to_length() is incorrectly using div_u64()
> instead of div64_u64().
> ---
>  net/sched/sch_taprio.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 1ab17e8a72605385280fad9b7f656a6771236acc..827fb81fc63a098304bad198fadd4aed55d1fec4 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -256,7 +256,8 @@ static int length_to_duration(struct taprio_sched *q, int len)
>  
>  static int duration_to_length(struct taprio_sched *q, u64 duration)
>  {
> -	return div_u64(duration * PSEC_PER_NSEC, atomic64_read(&q->picos_per_byte));
> +	return div64_u64(duration * PSEC_PER_NSEC,
> +			 atomic64_read(&q->picos_per_byte));
>  }

There's a netdev_dbg() in taprio_set_picos_per_byte(). Could you turn
that on? I'm curious what was the q->picos_per_byte value that triggered
the 64-bit division fault. There are a few weird things about
q->picos_per_byte's representation and use as an atomic64_t (s64) type.