Make dnstap work reliably with netmgr

The introduction of netmgr doubled the number of threads from which
dnstap data may be logged: previously, it could only happen from within
taskmgr worker threads; with netmgr, it can happen both from taskmgr
worker threads and from network threads.  Since the argument passed to
fstrm_iothr_options_set_num_input_queues() was not updated to reflect
this change, some calls to fstrm_iothr_get_input_queue() can now return
NULL, effectively preventing some dnstap data from being logged.
Whether this bug is triggered or not depends on thread scheduling order
and packet distribution between network threads, but will almost
certainly be triggered on any recursive resolver sooner or later.  Fix
by requesting the correct number of dnstap input queues to be allocated.

diff --git a/bin/named/server.c b/bin/named/server.c
index 0ff543e238e91b7bf9d4c6c81695d1ae1c5919ce..a3453d5fc206b12dc986ac1409c778cf3c3e178d 100644 (file)
--- a/bin/named/server.c
+++ b/bin/named/server.c
@@ -3677,7 +3677,11 @@ configure_dnstap(const cfg_obj_t **maps, dns_view_t *view) {
                }
 
                fopt = fstrm_iothr_options_init();
-               fstrm_iothr_options_set_num_input_queues(fopt, named_g_cpus);
+               /*
+                * Both network threads and worker threads may log dnstap data.
+                */
+               fstrm_iothr_options_set_num_input_queues(fopt,
+                                                        2 * named_g_cpus);
                fstrm_iothr_options_set_queue_model(
                        fopt, FSTRM_IOTHR_QUEUE_MODEL_MPSC);
 

diff --git a/bin/tests/system/dnstap/ns3/named.args b/bin/tests/system/dnstap/ns3/named.args
new file mode 100644 (file)
index 0000000..b746de5
--- /dev/null
+++ b/bin/tests/system/dnstap/ns3/named.args
@@ -0,0 +1,2 @@
+# Using "-n 1" allows GL #1795 to be reliably reproduced
+-D dnstap-ns3 -X named.lock -m record,size,mctx -c named.conf -d 99 -g -U 4 -n 1

diff --git a/util/copyrights b/util/copyrights
index e13441fee792954ce38ff1cbfe68488bdebb8289..6b4854027829e1019845cd5a12006ff0dde4f200 100644 (file)
--- a/util/copyrights
+++ b/util/copyrights
@@ -413,6 +413,7 @@
 ./bin/tests/system/dnstap/README               TXT.BRIEF       2019,2020
 ./bin/tests/system/dnstap/clean.sh             SH      2015,2016,2017,2018,2019,2020
 ./bin/tests/system/dnstap/large-answer.fstrm   X       2019,2020
+./bin/tests/system/dnstap/ns3/named.args       X       2020
 ./bin/tests/system/dnstap/setup.sh             SH      2018,2019,2020
 ./bin/tests/system/dnstap/tests.sh             SH      2015,2016,2017,2018,2019,2020
 ./bin/tests/system/dnstap/ydump.py             PYTHON  2016,2017,2018,2019,2020