0002-Fix-known-but-not-problematic-buffer-access-violatio.patch

From 9d5e5c61d4c954a71acca07ec37066b8ca5b4822 Mon Sep 17 00:00:00 2001
From: Asim R P <apraveen@pivotal.io>
Date: Wed, 18 Jul 2018 18:30:41 -0700
Subject: [PATCH 2/2] Fix known but not problematic buffer access violations

This is needed to make regression tests pass with
CFLAGS=-DMPROTECT_BUFFERS.
---
 src/backend/commands/sequence.c           |  3 ++-
 src/backend/storage/freespace/freespace.c | 11 ++++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 89122d4ad7..f44fb8c563 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -348,13 +348,14 @@ fill_seq_with_data(Relation rel, HeapTuple tuple)
 
 	page = BufferGetPage(buf);
 
+	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+
 	PageInit(page, BufferGetPageSize(buf), sizeof(sequence_magic));
 	sm = (sequence_magic *) PageGetSpecialPointer(page);
 	sm->magic = SEQ_MAGIC;
 
 	/* Now insert sequence tuple */
 
-	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
 
 	/*
 	 * Since VACUUM does not process sequences, we have to force the tuple to
diff --git a/src/backend/storage/freespace/freespace.c b/src/backend/storage/freespace/freespace.c
index 8d0ee7fc93..df813d7416 100644
--- a/src/backend/storage/freespace/freespace.c
+++ b/src/backend/storage/freespace/freespace.c
@@ -901,8 +901,17 @@ fsm_vacuum_page(Relation rel, FSMAddress addr,
 	 * relation.  We don't bother with a lock here, nor with marking the page
 	 * dirty if it wasn't already, since this is just a hint.
 	 */
+#ifdef MPROTECT_BUFFERS
+	/*
+	 * When mprotect() is used to detect shared buffer access violations, lock
+	 * must be acquired so that write access is allowed on this buffer.
+	 */
+	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+#endif
 	((FSMPage) PageGetContents(page))->fp_next_slot = 0;
-
+#ifdef MPROTECT_BUFFERS
+	LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+#endif
 	ReleaseBuffer(buf);
 
 	return max_avail;
-- 
2.17.1