From: Colin Vidal <colin@isc.org>
Date: Thu, 15 Jan 2026 09:42:13 +0000 (+0100)
Subject: resolver: Defer cloning of fetch responses until events are sent
X-Git-Tag: v9.21.19~30^2~6
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=74a74b5f29b0c4208ad4c55f2f704ee6879d3960;p=thirdparty%2Fbind9.git

resolver: Defer cloning of fetch responses until events are sent

Instead of cloning fetch responses immediately after writing to the
head of the fetch response list, defer cloning until the events are
actually sent.

This removes the need for the `fctx->cloned` state. However, a new
fetch state value, fetchstate_sentevents, is introduced and occurs
after fetchstate_done.  To prevent new fetch responses from being
prepended after the head is written but before cloning occurs,
fetchstate_done is now set at all call sites that previously invoked
`clone_results()`.
---

diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index 919e518ac96..4fe66e4b6e0 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -299,8 +299,9 @@ struct tried {
 #define RESQUERY_SENDING(q)    ((q)->sends > 0)
 
 typedef enum {
-	fetchstate_active,
-	fetchstate_done /*%< Fetch completion events posted. */
+	fetchstate_active = 0,
+	fetchstate_done,
+	fetchstate_sendevents /*%< Fetch completion events posted. */
 } fetchstate_t;
 
 typedef enum {
@@ -350,7 +351,6 @@ struct fetchctx {
 	/*% Locked by lock. */
 	isc_mutex_t lock;
 	fetchstate_t state;
-	bool cloned;
 	bool spilled;
 	uint_fast32_t allowed;
 	uint_fast32_t dropped;
@@ -496,7 +496,7 @@ struct fetchctx {
 	((atomic_load_acquire(&(f)->attributes) & FCTX_ATTR_GLUING) != 0)
 #define ADDRWAIT(f) \
 	((atomic_load_acquire(&(f)->attributes) & FCTX_ATTR_ADDRWAIT) != 0)
-#define SHUTTINGDOWN(f) ((f)->state == fetchstate_done)
+#define SHUTTINGDOWN(f) ((f)->state >= fetchstate_done)
 #define WANTCACHE(f) \
 	((atomic_load_acquire(&(f)->attributes) & FCTX_ATTR_WANTCACHE) != 0)
 #define WANTNCACHE(f) \
@@ -806,9 +806,6 @@ fctx__done(fetchctx_t *fctx, isc_result_t result, const char *func,
 static void
 resume_qmin(void *arg);
 
-static void
-clone_results(fetchctx_t *fctx);
-
 static isc_result_t
 get_attached_fctx(dns_resolver_t *res, isc_loop_t *loop, const dns_name_t *name,
 		  dns_rdatatype_t type, const dns_name_t *domain,
@@ -1615,6 +1612,48 @@ fcount_decr(fetchctx_t *fctx) {
 static void
 spillattimer_countdown(void *arg);
 
+static void
+clone_results(fetchctx_t *fctx) {
+	dns_fetchresponse_t *hresp = NULL;
+
+	REQUIRE(!ISC_LIST_EMPTY(fctx->resps));
+
+	/*
+	 * Set up any other resps to have the same data as the first.
+	 * Caller must be holding the appropriate lock.
+	 */
+
+	FCTXTRACE("clone_results");
+
+	ISC_LIST_FOREACH(fctx->resps, resp, link) {
+		/* This is the head resp; keep a pointer and move on */
+		if (hresp == NULL) {
+			hresp = ISC_LIST_HEAD(fctx->resps);
+			FCTXTRACEN("clone_results", hresp->foundname,
+				   hresp->result);
+			continue;
+		}
+
+		resp->result = hresp->result;
+		dns_name_copy(hresp->foundname, resp->foundname);
+		dns_db_attach(hresp->db, &resp->db);
+		dns_db_attachnode(hresp->node, &resp->node);
+
+		INSIST(hresp->rdataset != NULL && resp->rdataset != NULL);
+		if (dns_rdataset_isassociated(hresp->rdataset)) {
+			dns_rdataset_clone(hresp->rdataset, resp->rdataset);
+		}
+
+		INSIST(hresp->sigrdataset != NULL || resp->sigrdataset == NULL);
+		if (resp->sigrdataset != NULL && hresp->sigrdataset != NULL &&
+		    dns_rdataset_isassociated(hresp->sigrdataset))
+		{
+			dns_rdataset_clone(hresp->sigrdataset,
+					   resp->sigrdataset);
+		}
+	}
+}
+
 static void
 fctx_sendevents(fetchctx_t *fctx, isc_result_t result) {
 	unsigned int count = 0;
@@ -1626,8 +1665,11 @@ fctx_sendevents(fetchctx_t *fctx, isc_result_t result) {
 
 	LOCK(&fctx->lock);
 
-	REQUIRE(fctx->state == fetchstate_done);
+	REQUIRE(fctx->state == fetchstate_sendevents);
 
+	if (result == ISC_R_SUCCESS) {
+		clone_results(fctx);
+	}
 	FCTXTRACE("sendevents");
 
 	/*
@@ -1760,11 +1802,11 @@ fctx__done(fetchctx_t *fctx, isc_result_t result, const char *func,
 		LOCK(&fctx->lock);
 	}
 	/* We need to do this under the lock for intra-thread synchronization */
-	if (fctx->state == fetchstate_done) {
+	if (fctx->state == fetchstate_sendevents) {
 		UNLOCK(&fctx->lock);
 		return false;
 	}
-	fctx->state = fetchstate_done;
+	fctx->state = fetchstate_sendevents;
 	FCTX_ATTR_CLR(fctx, FCTX_ATTR_ADDRWAIT);
 
 	/* The fctx will get deleted either here or in get_attached_fctx() */
@@ -4390,7 +4432,7 @@ resume_qmin(void *arg) {
 					dns_db_attachnode(node, &resp->node);
 				}
 				dns_name_copy(fname, resp->foundname);
-				clone_results(fctx);
+				fctx->state = fetchstate_done;
 				UNLOCK(&fctx->lock);
 				goto cleanup;
 			}
@@ -4457,7 +4499,7 @@ resume_qmin(void *arg) {
 					dns_db_attachnode(node, &resp->node);
 				}
 				dns_name_copy(fname, resp->foundname);
-				clone_results(fctx);
+				fctx->state = fetchstate_done;
 				if (result == DNS_R_CNAME &&
 				    dns_rdataset_isassociated(&rdataset) &&
 				    fctx->type == dns_rdatatype_cname)
@@ -5243,50 +5285,6 @@ same_question(fetchctx_t *fctx, dns_message_t *message) {
 	return ISC_R_SUCCESS;
 }
 
-static void
-clone_results(fetchctx_t *fctx) {
-	dns_fetchresponse_t *hresp = NULL;
-
-	REQUIRE(!ISC_LIST_EMPTY(fctx->resps));
-
-	/*
-	 * Set up any other resps to have the same data as the first.
-	 * Caller must be holding the appropriate lock.
-	 */
-
-	FCTXTRACE("clone_results");
-
-	ISC_LIST_FOREACH(fctx->resps, resp, link) {
-		/* This is the head resp; keep a pointer and move on */
-		if (hresp == NULL) {
-			hresp = ISC_LIST_HEAD(fctx->resps);
-			FCTXTRACEN("clone_results", hresp->foundname,
-				   hresp->result);
-			continue;
-		}
-
-		resp->result = hresp->result;
-		dns_name_copy(hresp->foundname, resp->foundname);
-		dns_db_attach(hresp->db, &resp->db);
-		dns_db_attachnode(hresp->node, &resp->node);
-
-		INSIST(hresp->rdataset != NULL && resp->rdataset != NULL);
-		if (dns_rdataset_isassociated(hresp->rdataset)) {
-			dns_rdataset_clone(hresp->rdataset, resp->rdataset);
-		}
-
-		INSIST(hresp->sigrdataset != NULL || resp->sigrdataset == NULL);
-		if (resp->sigrdataset != NULL && hresp->sigrdataset != NULL &&
-		    dns_rdataset_isassociated(hresp->sigrdataset))
-		{
-			dns_rdataset_clone(hresp->sigrdataset,
-					   resp->sigrdataset);
-		}
-	}
-
-	fctx->cloned = true;
-}
-
 #define CACHE(r)      (((r)->attributes.cache))
 #define ANSWER(r)     (((r)->attributes.answer))
 #define ANSWERSIG(r)  (((r)->attributes.answersig))
@@ -5794,7 +5792,7 @@ answer_response:
 		dns_name_copy(val->name, resp->foundname);
 		dns_db_attach(fctx->cache, &resp->db);
 		dns_db_transfernode(fctx->cache, &node, &resp->node);
-		clone_results(fctx);
+		fctx->state = fetchstate_done;
 	}
 
 	done = true;
@@ -6250,8 +6248,7 @@ rctx_cachename(respctx_t *rctx, dns_message_t *message, dns_name_t *name) {
 			dns_name_copy(name, resp->foundname);
 			dns_db_attach(fctx->cache, &resp->db);
 			dns_db_transfernode(fctx->cache, &node, &resp->node);
-			clone_results(fctx);
-
+			fctx->state = fetchstate_done;
 			FCTX_ATTR_SET(fctx, FCTX_ATTR_HAVEANSWER);
 		}
 	}
@@ -6442,7 +6439,7 @@ rctx_ncache(respctx_t *rctx) {
 		dns_name_copy(name, resp->foundname);
 		dns_db_attach(fctx->cache, &resp->db);
 		dns_db_transfernode(fctx->cache, &node, &resp->node);
-		clone_results(fctx);
+		fctx->state = fetchstate_done;
 	}
 
 unlock:
@@ -10164,7 +10161,7 @@ get_attached_fctx(dns_resolver_t *res, isc_loop_t *loop, const dns_name_t *name,
 		goto create;
 	}
 
-	if (SHUTTINGDOWN(fctx) || fctx->cloned) {
+	if (SHUTTINGDOWN(fctx)) {
 		/* The fctx will get deleted either here or in fctx__done() */
 		cds_lfht_del(res->fctxs_ht, &fctx->ht_node);
 
@@ -10419,7 +10416,7 @@ dns_resolver_destroyfetch(dns_fetch_t **fetchp) {
 	 * Sanity check: the caller should have gotten its event before
 	 * trying to destroy the fetch.
 	 */
-	if (fctx->state != fetchstate_done) {
+	if (!SHUTTINGDOWN(fctx)) {
 		ISC_LIST_FOREACH(fctx->resps, resp, link) {
 			RUNTIME_CHECK(resp->fetch != fetch);
 		}
@@ -10721,6 +10718,8 @@ dns_resolver_dumpfetches(dns_resolver_t *res, isc_statsformat_t format,
 		char typebuf[DNS_RDATATYPE_FORMATSIZE];
 		char timebuf[1024];
 		unsigned int resp_count = 0, query_count = 0;
+		const char *fetchstatestr[] = { "active", "done",
+						"sendevents" };
 
 		LOCK(&fctx->lock);
 		dns_name_print(fctx->name, fp);
@@ -10731,10 +10730,7 @@ dns_resolver_dumpfetches(dns_resolver_t *res, isc_statsformat_t format,
 		dns_rdatatype_format(fctx->type, typebuf, sizeof(typebuf));
 
 		fprintf(fp, "/%s (%s), 0x%x: started %s, ", typebuf,
-			fctx->state == fetchstate_done ? "done"
-			: fctx->cloned		       ? "cloned"
-						       : "active",
-			fctx->options, timebuf);
+			fetchstatestr[fctx->state], fctx->options, timebuf);
 
 		ISC_LIST_FOREACH(fctx->resps, resp, link) {
 			resp_count++;