1 files changed, 42 insertions, 11 deletions

diff --git a/src/backend/access/gin/ginbtree.c b/src/backend/access/gin/ginbtree.c
index f032faa22ec..010812dc6d3 100644
--- a/src/backend/access/gin/ginbtree.c
+++ b/src/backend/access/gin/ginbtree.c
@@ -112,10 +112,8 @@ ginFindLeafPage(GinBtree btree, GinBtreeStack *stack)
 				/* rightmost page */
 				break;
 
+			stack->buffer = ginStepRight(stack->buffer, btree->index, access);
 			stack->blkno = rightlink;
-			LockBuffer(stack->buffer, GIN_UNLOCK);
-			stack->buffer = ReleaseAndReadBuffer(stack->buffer, btree->index, stack->blkno);
-			LockBuffer(stack->buffer, access);
 			page = BufferGetPage(stack->buffer);
 		}
 
@@ -148,6 +146,41 @@ ginFindLeafPage(GinBtree btree, GinBtreeStack *stack)
 	}
 }
 
+/*
+ * Step right from current page.
+ *
+ * The next page is locked first, before releasing the current page. This is
+ * crucial to protect from concurrent page deletion (see comment in
+ * ginDeletePage).
+ */
+Buffer
+ginStepRight(Buffer buffer, Relation index, int lockmode)
+{
+	Buffer		nextbuffer;
+	Page		page = BufferGetPage(buffer);
+	bool		isLeaf = GinPageIsLeaf(page);
+	bool		isData = GinPageIsData(page);
+	BlockNumber	blkno = GinPageGetOpaque(page)->rightlink;
+
+	nextbuffer = ReadBuffer(index, blkno);
+	LockBuffer(nextbuffer, lockmode);
+	UnlockReleaseBuffer(buffer);
+
+	/* Sanity check that the page we stepped to is of similar kind. */
+	page = BufferGetPage(nextbuffer);
+	if (isLeaf != GinPageIsLeaf(page) || isData != GinPageIsData(page))
+		elog(ERROR, "right sibling of GIN page is of different type");
+
+	/*
+	 * Given the proper lock sequence above, we should never land on a
+	 * deleted page.
+	 */
+	if  (GinPageIsDeleted(page))
+		elog(ERROR, "right sibling of GIN page was deleted");
+
+	return nextbuffer;
+}
+
 void
 freeGinBtreeStack(GinBtreeStack *stack)
 {
@@ -235,12 +268,12 @@ ginFindParents(GinBtree btree, GinBtreeStack *stack,
 		while ((offset = btree->findChildPtr(btree, page, stack->blkno, InvalidOffsetNumber)) == InvalidOffsetNumber)
 		{
 			blkno = GinPageGetOpaque(page)->rightlink;
-			LockBuffer(buffer, GIN_UNLOCK);
-			ReleaseBuffer(buffer);
 			if (blkno == InvalidBlockNumber)
+			{
+				UnlockReleaseBuffer(buffer);
 				break;
-			buffer = ReadBuffer(btree->index, blkno);
-			LockBuffer(buffer, GIN_EXCLUSIVE);
+			}
+			buffer = ginStepRight(buffer, btree->index, GIN_EXCLUSIVE);
 			page = BufferGetPage(buffer);
 		}
 
@@ -444,23 +477,21 @@ ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
 		{
 			BlockNumber rightlink = GinPageGetOpaque(page)->rightlink;
 
-			LockBuffer(parent->buffer, GIN_UNLOCK);
-
 			if (rightlink == InvalidBlockNumber)
 			{
 				/*
 				 * rightmost page, but we don't find parent, we should use
 				 * plain search...
 				 */
+				LockBuffer(parent->buffer, GIN_UNLOCK);
 				ginFindParents(btree, stack, rootBlkno);
 				parent = stack->parent;
 				Assert(parent != NULL);
 				break;
 			}
 
+			parent->buffer = ginStepRight(parent->buffer, btree->index, GIN_EXCLUSIVE);
 			parent->blkno = rightlink;
-			parent->buffer = ReleaseAndReadBuffer(parent->buffer, btree->index, parent->blkno);
-			LockBuffer(parent->buffer, GIN_EXCLUSIVE);
 			page = BufferGetPage(parent->buffer);
 		}