[PATCH v2 2/5] eal: fix async IPC callback not fired when no peers

[Burakov, Anatoly]

On 6/1/2026 2:40 PM, Thomas Monjalon wrote:
> 01/06/2026 14:21, Thomas Monjalon:
>> 29/05/2026 17:26, Anatoly Burakov:
>>> Currently, when rte_mp_request_async() is called and no peer processes
>>> are connected (nb_sent == 0), the user callback is never invoked.
>>>
>>> The original implementation used a dedicated background thread and
>>> pthread_cond_signal() to wake it after queuing the dummy request. When
>>> that thread was replaced with per-message alarms, no alarm was set for
>>> the dummy request, silently breaking the nb_sent == 0 path.
>>>
>>> This was not noticed because async requests are used while handling
>>> secondary process requests, where peers are typically already present.
>>>
>>> Fix it by setting a 1us alarm on the dummy request, so the callback path
>>> immediately triggers and processes it.
>>>
>>> Fixes: daf9bfca717e ("ipc: remove thread for async requests")
>>> Cc: stable at dpdk.org
>>>
>>> Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
>>> ---
>>>   lib/eal/common/eal_common_proc.c | 12 ++++++++++--
>>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/eal/common/eal_common_proc.c b/lib/eal/common/eal_common_proc.c
>>> index 799c6e81b0..0ec79336a5 100644
>>> --- a/lib/eal/common/eal_common_proc.c
>>> +++ b/lib/eal/common/eal_common_proc.c
>>> @@ -1187,11 +1187,15 @@ rte_mp_request_async(struct rte_mp_msg *req, const struct timespec *ts,
>>>   	if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
>>>   		ret = mp_request_async(eal_mp_socket_path(), copy, param, ts);
>>>   
>>> -		/* if we didn't send anything, put dummy request on the queue */
>>> +		/* if we didn't send anything, put dummy request on the queue
>>> +		 * and set a minimum-delay alarm so the callback fires immediately.
>>> +		 */
>>>   		if (ret == 0 && reply->nb_sent == 0) {
>>>   			TAILQ_INSERT_TAIL(&pending_requests.requests, dummy,
>>>   					next);
>>>   			dummy_used = true;
>>> +			if (rte_eal_alarm_set(1, async_reply_handle, dummy) < 0)
>>> +				EAL_LOG(ERR, "Fail to set alarm for dummy request");
>>
>> Shouldn't we return an error?
> 
> AI suggests this:
> 
>        if (rte_eal_alarm_set(1, async_reply_handle,
>                (void *)(uintptr_t)dummy->id) < 0) {
>            EAL_LOG(ERR, "Fail to set alarm for dummy request");
>            TAILQ_REMOVE(&pending_requests.requests, dummy, next);
>            dummy_used = false;
>            ret = -1;
>        }
> 
Dummy id is not added till later in the series, but I'll integrate this 
otherwise.

-- 
Thanks,
Anatoly