Re: [PATCH] ratelimit: restrict the delay time to a non-negative value

[Alberto Garcia <berto@igalia.com>]

On Wed 21 Sep 2022 09:47:32 AM +08, Wang Liang wrote:
>> > -    return limit->slice_end_time - now;
>> > +    return MAX(limit->slice_end_time - now, 0);
>> 
>> How can this be negative? slice_end_time is guaranteed to be larger
>> than
>> now:
>> 
>>     if (limit->slice_end_time < now) {
>>         /* Previous, possibly extended, time slice finished; reset
>> the
>>          * accounting. */
>>         limit->slice_start_time = now;
>>         limit->slice_end_time = now + limit->slice_ns;
>>         limit->dispatched = 0;
>>     }
>> 
> This is just a guarantee. 
>
> If slice_end_time is assigned later by
>     limit->slice_end_time = limit->slice_start_time +
>         (uint64_t)(delay_slices * limit->slice_ns);

Ok, on a closer look, if at the start of the function

   limit->slice_start_time < now, and
   limit->slice_end_time >= now

it seems that in principle what you say can happen.

If it's so, it would be good to know under what conditions this happens,
because this hasn't changed in years.

Berto