From 7c8345f67f3008a394adccae262f2a2162b6f5c7 Mon Sep 17 00:00:00 2001
From: Teodor Sigaev <teodor@sigaev.ru>
Date: Tue, 17 May 2016 00:01:35 +0300
Subject: [PATCH] Correctly align page's images in generic wal API

Page image should be MAXALIGN'ed because existing code could directly align
pointers in page instead of align offset from beginning of page.

Found during play with indexes as extenstion, Alexander Korotkov and me
---
 src/backend/access/transam/generic_xlog.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/transam/generic_xlog.c b/src/backend/access/transam/generic_xlog.c
index 6e213e2f60c..8ad69f83b1f 100644
--- a/src/backend/access/transam/generic_xlog.c
+++ b/src/backend/access/transam/generic_xlog.c
@@ -52,7 +52,9 @@ typedef struct
 	Buffer		buffer;			/* registered buffer */
 	int			flags;			/* flags for this buffer */
 	int			deltaLen;		/* space consumed in delta field */
-	char		image[BLCKSZ];	/* copy of page image for modification */
+	char		*image;			/* copy of page image for modification,
+								 * do not do it in-place to have aligned
+								 * memory chunk */
 	char		delta[MAX_DELTA_SIZE];	/* delta between page images */
 } PageData;
 
@@ -268,7 +270,15 @@ GenericXLogStart(Relation relation)
 
 	state->isLogged = RelationNeedsWAL(relation);
 	for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+	{
+		/*
+		 * pre-alloc page's images to prevent allocation in
+		 * GenericXLogRegisterBuffer() which could be called in different
+		 * memory context(s)
+		 */
+		state->pages[i].image = palloc(BLCKSZ);
 		state->pages[i].buffer = InvalidBuffer;
+	}
 
 	return state;
 }
@@ -422,6 +432,8 @@ GenericXLogFinish(GenericXLogState *state)
 		lsn = InvalidXLogRecPtr;
 	}
 
+	for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+		pfree(state->pages[i].image);
 	pfree(state);
 
 	return lsn;