commit 5f7c62fa4d1a3b756119f7e279c5753036c3e9d1
from: Martijn van Duren <martijn@openbsd.org>
date: Mon Mar 28 14:16:09 2022 UTC

pause stdout io when handling input.
It's not going to be scheduled while we're still in the parsing input codepath
and it causes a massive build-up of the kevent array in libevent, resulting in
high memory usage never released.

commit - 24587d39df0893249ec70e21ad4c1ae6384587f1
commit + 5f7c62fa4d1a3b756119f7e279c5753036c3e9d1
blob - 1aec59c37c55b000486f0ae246b34a8dfdc7b3e8
blob + 71b0691f55d1ae2f533b94e0f027e22cf510c52e
--- opensmtpd.c
+++ opensmtpd.c
@@ -1029,6 +1029,11 @@ osmtpd_newline(struct io *io, int ev, __unused void *a
 	}
 	if (ev != IO_DATAIN)
 		return;
+	/*
+	 * Multiple calls to io_printf (through osmtpd_filter_dataline) can
+	 * cause a build-up of kevents, because of event_add/event_del loop.
+	 */
+	io_pause(io_stdout, IO_OUT);
 	while ((line = io_getline(io, &linelen)) != NULL) {
 		if (dupsize < linelen) {
 			if ((linedup = realloc(linedup, linelen + 1)) == NULL)
@@ -1189,6 +1194,7 @@ osmtpd_newline(struct io *io, int ev, __unused void *a
 		osmtpd_callbacks[i].osmtpd_cb(&(osmtpd_callbacks[i]),
 		    &(ctx->ctx), line, linedup);
 	}
+	io_resume(io_stdout, IO_OUT);
 }
 
 static void