update: mutex avoid next update before cleanup by call_rcu

src/knot/updates/apply.c

-/*  Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+/*  Copyright (C) 2019 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -418,6 +418,10 @@ void update_cleanup(apply_ctx_t *ctx)
 	// also the nodes not being affected by the update itself
 	// might be affected
 	zone_trees_unify_binodes(ctx->contents->nodes, ctx->contents->nsec3_nodes);
+
+	if (ctx->cow_mutex != NULL) {
+		pthread_mutex_unlock(ctx->cow_mutex);
+	}
 }
 
 void update_rollback(apply_ctx_t *ctx)
@@ -442,6 +446,10 @@ void update_rollback(apply_ctx_t *ctx)
 		trie_cow_rollback(ctx->contents->nsec3_nodes->cow, trie_cb_noop, NULL);
 	}
 
+	if (ctx->cow_mutex != NULL) {
+		pthread_mutex_unlock(ctx->cow_mutex);
+	}
+
 	free(ctx->contents->nodes);
 	free(ctx->contents->nsec3_nodes);
 

src/knot/updates/apply.h

-/*  Copyright (C) 2017 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+/*  Copyright (C) 2019 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <pthread.h>
+
 #include "knot/zone/contents.h"
 #include "knot/updates/changesets.h"
 #include "contrib/ucw/lists.h"
@@ -29,6 +31,7 @@ struct apply_ctx {
 	zone_tree_t *node_ptrs;   /*!< Just pointers to the affected nodes in contents. */
 	zone_tree_t *nsec3_ptrs;  /*!< The same for NSEC3 nodes. */
 	uint32_t flags;
+	pthread_mutex_t *cow_mutex; // pointer to zone_t struct
 };
 
 typedef struct apply_ctx apply_ctx_t;

src/knot/updates/zone-update.c

@@ -127,6 +127,9 @@ int init_base(zone_update_t *update, zone_t *zone, zone_contents_t *old_contents
 		return KNOT_ENOMEM;
 	}
 
+	pthread_mutex_lock(&zone->cow_lock);
+	update->a_ctx->cow_mutex = &zone->cow_lock;
+
 	int ret = KNOT_EINVAL;
 	if (flags & UPDATE_INCREMENTAL) {
 		ret = init_incremental(update, zone, old_contents, flags & UPDATE_JOURNAL);
@@ -134,6 +137,7 @@ int init_base(zone_update_t *update, zone_t *zone, zone_contents_t *old_contents
 		ret = init_full(update, zone);
 	}
 	if (ret != KNOT_EOK) {
+		pthread_mutex_unlock(&zone->cow_lock);
 		free(update->a_ctx);
 	}
 
@@ -217,6 +221,9 @@ int zone_update_from_contents(zone_update_t *update, zone_t *zone_without_conten
 		return KNOT_ENOMEM;
 	}
 
+	pthread_mutex_lock(&update->zone->cow_lock);
+	update->a_ctx->cow_mutex = &update->zone->cow_lock;
+
 	if (flags & UPDATE_INCREMENTAL) {
 		int ret = changeset_init(&update->change, zone_without_contents->name);
 		if (ret != KNOT_EOK) {
@@ -335,6 +342,9 @@ void zone_update_clear(zone_update_t *update)
 		update_cleanup(update->a_ctx);
 		zone_contents_deep_free(update->new_cont);
 	}
+	if (update->a_ctx != NULL && update->a_ctx->cow_mutex != NULL) {
+		pthread_mutex_unlock(update->a_ctx->cow_mutex);
+	}
 	free(update->a_ctx);
 	mp_delete(update->mm.ctx);
 	memset(update, 0, sizeof(*update));

src/knot/zone/zone.c

@@ -175,6 +175,8 @@ zone_t* zone_new(const knot_dname_t *name)
 	zone->ddns_queue_size = 0;
 	init_list(&zone->ddns_queue);
 
+	pthread_mutex_init(&zone->cow_lock, NULL);
+
 	// Preferred master lock
 	pthread_mutex_init(&zone->preferred_lock, NULL);
 
@@ -213,6 +215,9 @@ void zone_free(zone_t **zone_ptr)
 	free_ddns_queue(zone);
 	pthread_mutex_destroy(&zone->ddns_lock);
 
+	pthread_mutex_lock(&zone->cow_lock);
+	pthread_mutex_destroy(&zone->cow_lock);
+
 	/* Control update. */
 	zone_control_clear(zone);
 

src/knot/zone/zone.h

@@ -71,6 +71,9 @@ typedef struct zone
 	/*! \brief Control update context. */
 	struct zone_update *control_update;
 
+	/*! \brief Ensue one COW tramsaction on zone's trees at a time. */
+	pthread_mutex_t cow_lock;
+
 	/*! \brief Ptr to journal DB (in struct server) */
 	knot_lmdb_db_t *journaldb;
 

tests/knot/test_zone-update.c

@@ -15,6 +15,7 @@
  */
 
 #include <assert.h>
+#include <pthread.h>
 #include <tap/basic.h>
 #include <tap/files.h>
 #include <unistd.h>
@@ -105,9 +106,11 @@ static int test_node_unified(zone_node_t *n1, void *v)
 	return KNOT_EOK;
 }
 
-static void test_zone_unified(zone_contents_t *z)
+static void test_zone_unified(zone_t *z)
 {
-	zone_tree_apply(z->nodes, test_node_unified, NULL);
+	pthread_mutex_lock(&z->cow_lock);
+	zone_tree_apply(z->contents->nodes, test_node_unified, NULL);
+	pthread_mutex_unlock(&z->cow_lock);
 }
 
 void test_full(zone_t *zone, zs_scanner_t *sc)
@@ -223,7 +226,7 @@ void test_full(zone_t *zone, zs_scanner_t *sc)
 	rrset_present = node_contains_rr(node, &rrset);
 	ok(ret == KNOT_EOK && rrset_present, "full zone update: commit");
 
-	test_zone_unified(zone->contents);
+	test_zone_unified(zone);
 
 	knot_rdataset_clear(&rrset.rrs, NULL);
 }
@@ -325,7 +328,7 @@ void test_incremental(zone_t *zone, zs_scanner_t *sc)
 	rrset_present = node_contains_rr(iter_node, &rrset);
 	ok(ret == KNOT_EOK && rrset_present, "incremental zone update: commit");
 
-	test_zone_unified(zone->contents);
+	test_zone_unified(zone);
 
 	knot_rdataset_clear(&rrset.rrs, NULL);
 }