[PATCH v2 5/9] bpf: simplify callback inuse tracking to boolean flag

[Konstantin Ananyev]

>
> On 19/10/2026 21:50, Konstantin Ananyev wrote:
>>> The even/odd usage counter semantics in struct bpf_eth_cbi was
>>> originally used to detect when in-flight packet callbacks complete.
>>> However, with at most one thread running the callback per port/queue
>>> pair and no risk of the ABA problem, a boolean flag (true for in use,
>>> false for idle) suffices.
>>>
>>> Change member use to bool and replace the counter increment in the
>>> datapath with stores of true and false. Simplify bpf_eth_cbi_wait()
>>> to a direct pause loop waiting until the flag is false, removing the
>>> now unnecessary RTE_WAIT_UNTIL_MASKED macro and casts. Update the
>>> documentation and synchronization sequence diagram accordingly.
>>
>> As I explained in previous mail, it is not about even/odd.
>> It is about waiting while current 'quiscent' period will end.
>> By 'simplifying' that to use just boll values (0/1) you introduce
>> a live-lock in CP: it can be blocked for very long time waiting
>> while DP thread will keep processing packets.
>
> I do not think this explanation is correct. It was always waiting only 
> for the next value after the odd one, there are no cases where 
> anything else happens.
        /* in use, busy wait till current RX/TX iteration is finished */
         if ((puse & BPF_ETH_CBI_INUSE) != 0) {
                 RTE_WAIT_UNTIL_MASKED((__rte_atomic uint32_t 
*)(uintptr_t)&cbi->use,
                         UINT32_MAX, !=, puse, rte_memory_order_acquire);
         }

Here, we are waiting when 'puse' will become not equal to 'cbi->use'.
So, any value except current puse is good.