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

[Thomas Monjalon]

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;
      }