On Fri, 14 Jun 2024 21:55:02 +0100,
Kirill A. Korinsky <kirill@korins.ky> wrote:
> 
> tech@,
> 
> I noticed that event_asr_dispatch never checks the return of event_add,
> which can lead to a kind of deadlock when an application expects the
> callback to fire, but it doesn't fire because asr_run returned error, and it
> can't schedule the new attempt.
> 
> Here is a suggested diff that sets ar_errno and ar_h_errno and fires the
> callback.
> 

and here updated version of diff which setup all errno.

Thus, it also calls event_del but it returns non zero only when base is
missed, and it is impossible because eva->ev already used.

diff --git lib/libevent/event.c lib/libevent/event.c
index 26bc37dea76..d45604cc085 100644
--- lib/libevent/event.c
+++ lib/libevent/event.c
@@ -949,9 +949,18 @@ event_asr_dispatch(int fd __attribute__((__unused__)),
 		event_set(&eva->ev, ar.ar_fd,
 		    ar.ar_cond == ASR_WANT_READ ? EV_READ : EV_WRITE,
 		    event_asr_dispatch, eva);
+
 		tv.tv_sec = ar.ar_timeout / 1000;
 		tv.tv_usec = (ar.ar_timeout % 1000) * 1000;
-		event_add(&eva->ev, &tv);
+
+		if (event_add(&eva->ev, &tv)) {
+			ar.ar_errno = errno;
+			ar.ar_h_errno = NETDB_INTERNAL;
+			ar.ar_gai_errno = EAI_SYSTEM;
+			ar.ar_rrset_errno = NETDB_INTERNAL;
+			eva->cb(&ar, eva->arg);
+			free(eva);
+		}
 	}
 }
 


-- 
wbr, Kirill