From c1821ccf920a44d67284be462bb0ca6729235ef1 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Ond=C5=99ej=20Sur=C3=BD?= Date: Tue, 27 Jun 2023 08:26:12 +0200 Subject: [PATCH] Call rcu_barrier() five times in the isc__mem_destroy() Because rcu_barrier() needs to be called as many times as the number of nested call_rcu() calls (call_rcu() calls made from call_rcu thread), and currently there's no mechanism to detect whether there are more call_rcu callbacks scheduled, we simply call the rcu_barrier() multiple times. The overhead is negligible and it prevents rare assertion failures caused by the check for memory leaks in isc__mem_destroy(). --- lib/isc/mem.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/lib/isc/mem.c b/lib/isc/mem.c index 593b610890..b03e1122d0 100644 --- a/lib/isc/mem.c +++ b/lib/isc/mem.c @@ -582,9 +582,25 @@ isc__mem_destroy(isc_mem_t **ctxp FLARG) { /* * wait for asynchronous memory reclamation to complete - * before checking for memory leaks + * before checking for memory leaks. + * + * Because rcu_barrier() needs to be called as many times + * as the number of nested call_rcu() calls (call_rcu() + * calls made from call_rcu thread), and currently there's + * no mechanism to detect whether there are more call_rcu + * callbacks scheduled, we simply call the rcu_barrier() + * multiple times. The overhead is negligible and it + * prevents rare assertion failures caused by the check + * for memory leaks below. + * + * If there's more nested call_rcu() calls than five levels, + * we are doing something horribly wrong... */ rcu_barrier(); + rcu_barrier(); + rcu_barrier(); + rcu_barrier(); + rcu_barrier(); #if ISC_MEM_TRACKLINES if ((ctx->debugging & ISC_MEM_DEBUGTRACE) != 0) {