From 3a9738e9729445c29e44bb319af3ab7bca2983a0 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 27 Jun 2018 12:14:58 -0700
Subject: [PATCH] Check for interrupts inside nbtree page deletion code.

Author:
Reviewed-By:
Discussion: https://postgr.es/m/
Backpatch:
---
 src/backend/access/nbtree/nbtpage.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index a24e64156ab..6e395199d55 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -1443,6 +1443,7 @@ _bt_pagedel(Relation rel, Buffer buf)
 		rightsib_empty = false;
 		while (P_ISHALFDEAD(opaque))
 		{
+			/* will check for interrupts, once lock is released */
 			if (!_bt_unlink_halfdead_page(rel, buf, &rightsib_empty))
 			{
 				/* _bt_unlink_halfdead_page already released buffer */
@@ -1455,6 +1456,12 @@ _bt_pagedel(Relation rel, Buffer buf)
 
 		_bt_relbuf(rel, buf);
 
+		/*
+		 * Check here, as calling loops will have locks held, preventing
+		 * interrupts from being processed.
+		 */
+		CHECK_FOR_INTERRUPTS();
+
 		/*
 		 * The page has now been deleted. If its right sibling is completely
 		 * empty, it's possible that the reason we haven't deleted it earlier
@@ -1707,6 +1714,12 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
 
 	LockBuffer(leafbuf, BUFFER_LOCK_UNLOCK);
 
+	/*
+	 * Check here, as calling loops will have locks held, preventing
+	 * interrupts from being processed.
+	 */
+	CHECK_FOR_INTERRUPTS();
+
 	/*
 	 * If the leaf page still has a parent pointing to it (or a chain of
 	 * parents), we don't unlink the leaf page yet, but the topmost remaining
@@ -1766,6 +1779,13 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
 			/* step right one page */
 			leftsib = opaque->btpo_next;
 			_bt_relbuf(rel, lbuf);
+
+			/*
+			 * It'd be good to check for interrupts here, but it's not
+			 * entirely trivial to do so because a lock is always held. As the
+			 * code is presently unreachable...
+			 */
+
 			if (leftsib == P_NONE)
 			{
 				elog(LOG, "no left sibling (concurrent deletion?) of block %u in \"%s\"",
-- 
2.18.0.rc2.dirty