From 34653bc9833d9c95ed1c52bed1ff01c6193de17b Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 2 Feb 2018 18:26:07 -0500 Subject: [PATCH] Be more wary about shm_toc_lookup failure. Commit 445dbd82a basically missed the point of commit d46633506, which was that we shouldn't allow shm_toc_lookup() failure to lead to a core dump or assertion crash, because the odds of such a failure should never be considered negligible. It's correct that we can't expect the PARALLEL_KEY_ERROR_QUEUE TOC entry to be there if we have no workers. But if we have no workers, we're not going to do anything in this function with the lookup result anyway, so let's just skip it. That lets the code use the easy-to-prove-safe noError=false case, rather than anything requiring effort to review. Back-patch to v10, like the previous commit. Discussion: https://postgr.es/m/3647.1517601675@sss.pgh.pa.us --- src/backend/access/transam/parallel.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c index b09a02d9bae..cfa13b908bb 100644 --- a/src/backend/access/transam/parallel.c +++ b/src/backend/access/transam/parallel.c @@ -388,8 +388,6 @@ void ReinitializeParallelDSM(ParallelContext *pcxt) { FixedParallelState *fps; - char *error_queue_space; - int i; /* Wait for any old workers to exit. */ if (pcxt->nworkers_launched > 0) @@ -409,18 +407,23 @@ ReinitializeParallelDSM(ParallelContext *pcxt) fps->last_xlog_end = 0; /* Recreate error queues (if they exist). */ - error_queue_space = - shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, true); - Assert(pcxt->nworkers == 0 || error_queue_space != NULL); - for (i = 0; i < pcxt->nworkers; ++i) + if (pcxt->nworkers > 0) { - char *start; - shm_mq *mq; + char *error_queue_space; + int i; - start = error_queue_space + i * PARALLEL_ERROR_QUEUE_SIZE; - mq = shm_mq_create(start, PARALLEL_ERROR_QUEUE_SIZE); - shm_mq_set_receiver(mq, MyProc); - pcxt->worker[i].error_mqh = shm_mq_attach(mq, pcxt->seg, NULL); + error_queue_space = + shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, false); + for (i = 0; i < pcxt->nworkers; ++i) + { + char *start; + shm_mq *mq; + + start = error_queue_space + i * PARALLEL_ERROR_QUEUE_SIZE; + mq = shm_mq_create(start, PARALLEL_ERROR_QUEUE_SIZE); + shm_mq_set_receiver(mq, MyProc); + pcxt->worker[i].error_mqh = shm_mq_attach(mq, pcxt->seg, NULL); + } } }