From: Thomas Munro <tmunro@postgresql.org>
Date: Sat, 1 Feb 2020 01:29:13 +0000 (+1300)
Subject: Fix memory leak on DSM slot exhaustion.
X-Git-Tag: REL9_4_26~7
X-Git-Url: http://git.postgresql.org/gitweb/?a=commitdiff_plain;h=95936c795b9f086c2b413b5150d2993ac30354fa;p=postgresql.git

Fix memory leak on DSM slot exhaustion.

If we attempt to create a DSM segment when no slots are available,
we should return the memory to the operating system.  Previously
we did that if the DSM_CREATE_NULL_IF_MAXSEGMENTS flag was
passed in, but we didn't do it if an error was raised.  Repair.

Back-patch to 9.4, where DSM segments arrived.

Author: Thomas Munro
Reviewed-by: Robert Haas
Reported-by: Julian Backes
Discussion: https://postgr.es/m/CA%2BhUKGKAAoEw-R4om0d2YM4eqT1eGEi6%3DQot-3ceDR-SLiWVDw%40mail.gmail.com
---

diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index 0e5a0c399f3..ed0b1f15f7c 100644
--- a/src/backend/storage/ipc/dsm.c
+++ b/src/backend/storage/ipc/dsm.c
@@ -496,9 +496,18 @@ dsm_create(Size size)
 
 	/* Verify that we can support an additional mapping. */
 	if (nitems >= dsm_control->maxitems)
+	{
+		LWLockRelease(DynamicSharedMemoryControlLock);
+		dsm_impl_op(DSM_OP_DESTROY, seg->handle, 0, &seg->impl_private,
+					&seg->mapped_address, &seg->mapped_size, WARNING);
+		if (seg->resowner != NULL)
+			ResourceOwnerForgetDSM(seg->resowner, seg);
+		dlist_delete(&seg->node);
+		pfree(seg);
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
 				 errmsg("too many dynamic shared memory segments")));
+	}
 
 	/* Enter the handle into a new array slot. */
 	dsm_control->item[nitems].handle = seg->handle;