pgq/triggers: Fix crash in case invalidate happens from signal handler.

Currently code assumed the invalidate happens only from per-query checks,
but this seems not to be the case.

Fix it by moving reset code out from invalidate callback.

Also old code seemed to leak htab per full reset, because it assumed
to be located under cache context, but init code did not assign it there.

Thanks to Andrew Dunstan for the report.

2 files changed, 36 insertions, 35 deletions

diff --git a/sql/pgq/triggers/common.c b/sql/pgq/triggers/common.c
index fc3c3b32..9ec1e320 100644
--- a/sql/pgq/triggers/common.c
+++ b/sql/pgq/triggers/common.c
@@ -46,6 +46,7 @@ PG_MODULE_MAGIC;
  * primary key info
  */
 
+static bool tbl_cache_invalid;
 static MemoryContext tbl_cache_ctx;
 static HTAB *tbl_cache_map;
 
@@ -222,41 +223,40 @@ static void init_module(void)
 {
 	static int callback_init = 0;
 
-	/* htab can be occasinally dropped */
+	/* do full reset if requested */
+	if (tbl_cache_invalid) {
+		if (tbl_cache_map)
+			hash_destroy(tbl_cache_map);
+		if (tbl_cache_ctx)
+			MemoryContextDelete(tbl_cache_ctx);
+		tbl_cache_map = NULL;
+		tbl_cache_ctx = NULL;
+		tbl_cache_invalid = false;
+	}
+
+	/* re-initialize cache */
 	if (tbl_cache_ctx)
 		return;
 	init_cache();
 
 	/*
-	 * Init plans.
+	 * Rest is done only once.
 	 */
+
 	if (!pkey_plan)
 		init_pkey_plan();
 
-	/* this must be done only once */
 	if (!callback_init) {
 		CacheRegisterRelcacheCallback(relcache_reset_cb, (Datum)0);
 		callback_init = 1;
 	}
 }
 
-static void full_reset(void)
-{
-	if (tbl_cache_ctx) {
-		/* needed only if backend has HASH_STATISTICS set */
-		/* hash_destroy(tbl_cache_map); */
-		MemoryContextDelete(tbl_cache_ctx);
-		tbl_cache_map = NULL;
-		tbl_cache_ctx = NULL;
-	}
-}
-
 /*
  * Fill table information in hash table.
  */
-static struct PgqTableInfo *fill_tbl_info(Relation rel)
+static void fill_tbl_info(Relation rel, struct PgqTableInfo *info)
 {
-	struct PgqTableInfo *info;
 	StringInfo pkeys;
 	Datum values[1];
 	const char *name = pgq_find_table_name(rel);
@@ -265,6 +265,9 @@ static struct PgqTableInfo *fill_tbl_info(Relation rel)
 	bool isnull;
 	int res, i, attno;
 
+	/* allow reset ASAP, but ignore it in this call */
+	info->invalid = false;
+
 	/* load pkeys */
 	values[0] = ObjectIdGetDatum(rel->rd_id);
 	res = SPI_execute_plan(pkey_plan, values, NULL, false, 0);
@@ -272,13 +275,6 @@ static struct PgqTableInfo *fill_tbl_info(Relation rel)
 		elog(ERROR, "pkey_plan exec failed");
 
 	/*
-	 * SPI_execute_plan may launch reset callback, thus we need
-	 * to load the final position after calling it.
-	 */
-	init_module();
-	info = hash_search(tbl_cache_map, &rel->rd_id, HASH_ENTER, NULL);
-
-	/*
 	 * Fill info
 	 */
 
@@ -299,8 +295,6 @@ static struct PgqTableInfo *fill_tbl_info(Relation rel)
 		appendStringInfoString(pkeys, name);
 	}
 	info->pkey_list = MemoryContextStrdup(tbl_cache_ctx, pkeys->data);
-
-	return info;
 }
 
 static void free_info(struct PgqTableInfo *info)
@@ -310,32 +304,38 @@ static void free_info(struct PgqTableInfo *info)
 	pfree((void *)info->pkey_list);
 }
 
+/*
+ * the callback can be launched any time from signal callback,
+ * only minimal tagging can be done here.
+ */
 static void relcache_reset_cb(Datum arg, Oid relid)
 {
 	if (relid == InvalidOid) {
-		full_reset();
-	} else if (tbl_cache_map) {
+		tbl_cache_invalid = true;
+	} else if (tbl_cache_map && !tbl_cache_invalid) {
 		struct PgqTableInfo *entry;
 		entry = hash_search(tbl_cache_map, &relid, HASH_FIND, NULL);
-		if (entry) {
-			free_info(entry);
-			hash_search(tbl_cache_map, &relid, HASH_REMOVE, NULL);
-		}
+		if (entry)
+			entry->invalid = true;
 	}
 }
 
 /*
- * fetch insert plan from cache.
+ * fetch table struct from cache.
  */
 struct PgqTableInfo *pgq_find_table_info(Relation rel)
 {
 	struct PgqTableInfo *entry;
+	bool found = false;
 
 	init_module();
 
-	entry = hash_search(tbl_cache_map, &rel->rd_id, HASH_FIND, NULL);
-	if (!entry)
-		entry = fill_tbl_info(rel);
+	entry = hash_search(tbl_cache_map, &rel->rd_id, HASH_ENTER, &found);
+	if (!found || entry->invalid) {
+		if (found)
+			free_info(entry);
+		fill_tbl_info(rel, entry);
+	}
 
 	return entry;
 }
diff --git a/sql/pgq/triggers/common.h b/sql/pgq/triggers/common.h
index 0adaa7b1..f3e79489 100644
--- a/sql/pgq/triggers/common.h
+++ b/sql/pgq/triggers/common.h
@@ -39,6 +39,7 @@ struct PgqTableInfo {
 	const char *pkey_list;	/* pk column name list */
 	int *pkey_attno;	/* pk column positions */
 	char *table_name;	/* schema-quelified table name */
+	bool invalid;		/* set if the info was invalidated */
 };
 
 /* common.c */