postgres.git / summary / log / commit / refs

commit    957ff087c822c95f63df956e1a91c15614ecb2b4
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Fri Feb 02 23:26:07 2018 +0000
First released in: 11.0, 10.2

    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 a325933940d..9d4efc0f8fc 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -434,8 +434,6 @@ void
 ReinitializeParallelDSM(ParallelContext *pcxt)
 {
 	FixedParallelState *fps;
-	char	   *error_queue_space;
-	int			i;
 
 	/* Wait for any old workers to exit. */
 	if (pcxt->nworkers_launched > 0)
@@ -456,18 +454,23 @@ 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);
+		}
 	}
 }
 


[parent: bf641d337601]