Re: [PATCH v3 2/5] eal: fix async IPC callback not fired when no peers

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu,  4 Jun 2026 17:32:16 +0100
Anatoly Burakov <anatoly.burakov@intel.com> wrote:

> 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@dpdk.org
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
>  lib/eal/common/eal_common_proc.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/eal/common/eal_common_proc.c b/lib/eal/common/eal_common_proc.c
> index 799c6e81b0..5cc15a0f78 100644
> --- a/lib/eal/common/eal_common_proc.c
> +++ b/lib/eal/common/eal_common_proc.c
> @@ -1187,11 +1187,21 @@ 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");
> +				/* roll back the changes */
> +				TAILQ_REMOVE(&pending_requests.requests, dummy, next);
> +				dummy_used = false;
> +				ret = -1;
> +			}
>  		}
>  
>  		pthread_mutex_unlock(&pending_requests.lock);
> @@ -1232,10 +1242,14 @@ rte_mp_request_async(struct rte_mp_msg *req, const struct timespec *ts,
>  		} else if (mp_request_async(path, copy, param, ts))
>  			ret = -1;
>  	}
> -	/* 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_HEAD(&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");
>  	}
>  
>  	/* finally, unlock the queue */


AI spotted potential issue:

The bug in 2/5: in the primary-process path, if rte_eal_alarm_set() fails for the dummy request, the code only logs it.
The dummy stays on the queue with no alarm, the function returns 0 (success),
the callback never fires, and dummy/copy/param leak.

The secondary path right above it handles this correctly (rolls back, returns -1).
Fix is to make the primary path do the same. This corner is never fixed by the later patches.