From cd54ac9abe8d751373ecff64ee79d7b942a5be4d Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Tue, 22 Sep 2020 16:24:06 +1000
Subject: [PATCH] Address lock-order-inversion

    WARNING: ThreadSanitizer: lock-order-inversion (potential deadlock)
    Cycle in lock order graph: M1 (0x000000000001) => M2 (0x000000000002) => M1

    Mutex M2 acquired here while holding mutex M1 in thread T1:
    #0 pthread_rwlock_wrlock <null>
    #1 isc_rwlock_lock lib/isc/rwlock.c:52:4
    #2 zone_postload lib/dns/zone.c:5101:2
    #3 receive_secure_db lib/dns/zone.c:16206:11
    #4 dispatch lib/isc/task.c:1152:7
    #5 run lib/isc/task.c:1344:2

    Mutex M1 previously acquired by the same thread here:
    #0 pthread_mutex_lock <null>
    #1 receive_secure_db lib/dns/zone.c:16204:2
    #2 dispatch lib/isc/task.c:1152:7
    #3 run lib/isc/task.c:1344:2

    Mutex M1 acquired here while holding mutex M2 in thread T1:
    #0 pthread_mutex_lock <null>
    #1 get_raw_serial lib/dns/zone.c:2518:2
    #2 zone_gotwritehandle lib/dns/zone.c:2559:4
    #3 dispatch lib/isc/task.c:1152:7
    #4 run lib/isc/task.c:1344:2

    Mutex M2 previously acquired by the same thread here:
    #0 pthread_rwlock_rdlock <null>
    #1 isc_rwlock_lock lib/isc/rwlock.c:48:3
    #2 zone_gotwritehandle lib/dns/zone.c:2552:2
    #3 dispatch lib/isc/task.c:1152:7
    #4 run lib/isc/task.c:1344:2

    Thread T1 (running) created by main thread at:
    #0 pthread_create <null>
    #1 isc_thread_create lib/isc/pthreads/thread.c:73:8
    #2 isc_taskmgr_create lib/isc/task.c:1434:3
    #3 create_managers bin/named/main.c:915:11
    #4 setup bin/named/main.c:1223:11
    #5 main bin/named/main.c:1523:2

    SUMMARY: ThreadSanitizer: lock-order-inversion (potential deadlock) in pthread_rwlock_wrlock

(cherry picked from commit 1090876693470eedf69211d0fe71ba2c88160f45)
Conflict: NA
Reference: https://gitlab.isc.org/isc-projects/bind9/-/commit/cd54ac9abe8d751373ecff64ee79d7b942a5be4d
---
 lib/dns/zone.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index 096ff82f34..fd634af65f 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -2468,6 +2468,7 @@ zone_gotwritehandle(isc_task_t *task, isc_event_t *event) {
 	isc_result_t result = ISC_R_SUCCESS;
 	dns_dbversion_t *version = NULL;
 	dns_masterrawheader_t rawdata;
+	dns_db_t *db = NULL;
 
 	REQUIRE(DNS_ZONE_VALID(zone));
 	INSIST(task == zone->task);
@@ -2483,9 +2484,12 @@ zone_gotwritehandle(isc_task_t *task, isc_event_t *event) {
 	INSIST(zone != zone->raw);
 	ZONEDB_LOCK(&zone->dblock, isc_rwlocktype_read);
 	if (zone->db != NULL) {
+		dns_db_attach(zone->db, &db);
+	}
+	ZONEDB_UNLOCK(&zone->dblock, isc_rwlocktype_read);
+	if (db != NULL) {
 		const dns_master_style_t *output_style;
-
-		dns_db_currentversion(zone->db, &version);
+		dns_db_currentversion(db, &version);
 		dns_master_initrawheader(&rawdata);
 		if (inline_secure(zone))
 			get_raw_serial(zone->raw, &rawdata);
@@ -2495,15 +2499,18 @@ zone_gotwritehandle(isc_task_t *task, isc_event_t *event) {
 			output_style = zone->masterstyle;
 		else
 			output_style = &dns_master_style_default;
-		result = dns_master_dumpinc3(zone->mctx, zone->db, version,
+		result = dns_master_dumpinc3(zone->mctx, db, version,
 					     output_style, zone->masterfile,
 					     zone->task, dump_done, zone,
 					     &zone->dctx, zone->masterformat,
 					     &rawdata);
-		dns_db_closeversion(zone->db, &version, false);
-	} else
+		dns_db_closeversion(db, &version, false);
+	} else {
 		result = ISC_R_CANCELED;
-	ZONEDB_UNLOCK(&zone->dblock, isc_rwlocktype_read);
+	}
+	if (db != NULL) {
+		dns_db_detach(&db);
+	}
 	UNLOCK_ZONE(zone);
 	if (result != DNS_R_CONTINUE)
 		goto fail;
-- 
2.23.0

