Reproduce debug_query_string==NULL on parallel workers.

Certain background workers initiate parallel queries while
debug_query_string==NULL, at which point they attempted strlen(NULL) and
died to SIGSEGV.  Older debug_query_string observers allow NULL, so do
likewise in these newer ones.  Back-patch to v11, where commit
7de4a1bcc56f494acbd0d6e70781df877dc8ecb5 introduced the first of these.

Discussion: https://postgr.es/m/20201014022636.GA1962668@rfd.leadboat.com

diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 1aa2363f1a59f9a83d67929023d75539c4118e3f..286d2cc93f197daf2e850a3deee7f41bfb4a6e42 100644 (file)
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -1341,7 +1341,6 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
        BTLeader   *btleader = (BTLeader *) palloc0(sizeof(BTLeader));
        BufferUsage *bufferusage;
        bool            leaderparticipates = true;
-       char       *sharedquery;
        int                     querylen;
 
 #ifdef DISABLE_LEADER_PARTICIPATION
@@ -1404,9 +1403,14 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
        shm_toc_estimate_keys(&pcxt->estimator, 1);
 
        /* Finally, estimate PARALLEL_KEY_QUERY_TEXT space */
-       querylen = strlen(debug_query_string);
-       shm_toc_estimate_chunk(&pcxt->estimator, querylen + 1);
-       shm_toc_estimate_keys(&pcxt->estimator, 1);
+       if (debug_query_string)
+       {
+               querylen = strlen(debug_query_string);
+               shm_toc_estimate_chunk(&pcxt->estimator, querylen + 1);
+               shm_toc_estimate_keys(&pcxt->estimator, 1);
+       }
+       else
+               querylen = 0;                   /* keep compiler quiet */
 
        /* Everyone's had a chance to ask for space, so now create the DSM */
        InitializeParallelDSM(pcxt);
@@ -1470,9 +1474,14 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)
        }
 
        /* Store query string for workers */
-       sharedquery = (char *) shm_toc_allocate(pcxt->toc, querylen + 1);
-       memcpy(sharedquery, debug_query_string, querylen + 1);
-       shm_toc_insert(pcxt->toc, PARALLEL_KEY_QUERY_TEXT, sharedquery);
+       if (debug_query_string)
+       {
+               char       *sharedquery;
+
+               sharedquery = (char *) shm_toc_allocate(pcxt->toc, querylen + 1);
+               memcpy(sharedquery, debug_query_string, querylen + 1);
+               shm_toc_insert(pcxt->toc, PARALLEL_KEY_QUERY_TEXT, sharedquery);
+       }
 
        /* Allocate space for each worker's BufferUsage; no need to initialize */
        bufferusage = shm_toc_allocate(pcxt->toc,
@@ -1669,7 +1678,7 @@ _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc)
 #endif                                                 /* BTREE_BUILD_STATS */
 
        /* Set debug_query_string for individual workers first */
-       sharedquery = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, false);
+       sharedquery = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, true);
        debug_query_string = sharedquery;
 
        /* Report the query string from leader */