3 files changed, 49 insertions, 16 deletions

diff --git a/src/backend/access/heap/hio.c b/src/backend/access/heap/hio.c
index 27af323ed11..46c2fd31e04 100644
--- a/src/backend/access/heap/hio.c
+++ b/src/backend/access/heap/hio.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/hio.c,v 1.54 2004/12/31 21:59:16 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/hio.c,v 1.54.4.1 2005/05/07 21:32:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -247,13 +247,6 @@ RelationGetBufferForTuple(Relation relation, Size len,
 	buffer = ReadBuffer(relation, P_NEW);
 
 	/*
-	 * Release the file-extension lock; it's now OK for someone else to
-	 * extend the relation some more.
-	 */
-	if (needLock)
-		UnlockPage(relation, 0, ExclusiveLock);
-
-	/*
 	 * We can be certain that locking the otherBuffer first is OK, since
 	 * it must have a lower page number.
 	 */
@@ -261,9 +254,22 @@ RelationGetBufferForTuple(Relation relation, Size len,
 		LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE);
 
 	/*
-	 * We need to initialize the empty new page.
+	 * Now acquire lock on the new page.
 	 */
 	LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+	/*
+	 * Release the file-extension lock; it's now OK for someone else to
+	 * extend the relation some more.  Note that we cannot release this
+	 * lock before we have buffer lock on the new page, or we risk a
+	 * race condition against vacuumlazy.c --- see comments therein.
+	 */
+	if (needLock)
+		UnlockPage(relation, 0, ExclusiveLock);
+
+	/*
+	 * We need to initialize the empty new page.
+	 */
 	pageHeader = (Page) BufferGetPage(buffer);
 	Assert(PageIsNew((PageHeader) pageHeader));
 	PageInit(pageHeader, BufferGetPageSize(buffer), 0);
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index 3e2a9010a44..378c5f9d36f 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.81 2004/12/31 21:59:22 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.81.4.1 2005/05/07 21:32:53 tgl Exp $
  *
  *	NOTES
  *	   Postgres btree pages look like ordinary relation pages.	The opaque
@@ -491,18 +491,21 @@ _bt_getbuf(Relation rel, BlockNumber blkno, int access)
 
 		buf = ReadBuffer(rel, P_NEW);
 
+		/* Acquire buffer lock on new page */
+		LockBuffer(buf, BT_WRITE);
+
 		/*
-		 * Release the file-extension lock; it's now OK for someone else
-		 * to extend the relation some more.
+		 * Release the file-extension lock; it's now OK for someone else to
+		 * extend the relation some more.  Note that we cannot release this
+		 * lock before we have buffer lock on the new page, or we risk a
+		 * race condition against btvacuumcleanup --- see comments therein.
 		 */
 		if (needLock)
 			UnlockPage(rel, 0, ExclusiveLock);
 
-		/* Acquire appropriate buffer lock on new page */
-		LockBuffer(buf, access);
-
 		/* Initialize the new page before returning it */
 		page = BufferGetPage(buf);
+		Assert(PageIsNew((PageHeader) page));
 		_bt_pageinit(page, BufferGetPageSize(buf));
 	}
 
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index ba31abcbbfd..988cbc2a218 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.124 2004/12/31 21:59:22 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.124.4.1 2005/05/07 21:32:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -670,11 +670,35 @@ btvacuumcleanup(PG_FUNCTION_ARGS)
 	BlockNumber pages_deleted = 0;
 	MemoryContext mycontext;
 	MemoryContext oldcontext;
+	bool		needLock;
 
 	Assert(stats != NULL);
 
+	/*
+	 * First find out the number of pages in the index.  We must acquire
+	 * the relation-extension lock while doing this to avoid a race
+	 * condition: if someone else is extending the relation, there is
+	 * a window where bufmgr/smgr have created a new all-zero page but
+	 * it hasn't yet been write-locked by _bt_getbuf().  If we manage to
+	 * scan such a page here, we'll improperly assume it can be recycled.
+	 * Taking the lock synchronizes things enough to prevent a problem:
+	 * either num_pages won't include the new page, or _bt_getbuf already
+	 * has write lock on the buffer and it will be fully initialized before
+	 * we can examine it.  (See also vacuumlazy.c, which has the same issue.)
+	 *
+	 * We can skip locking for new or temp relations,
+	 * however, since no one else could be accessing them.
+	 */
+	needLock = !RELATION_IS_LOCAL(rel);
+
+	if (needLock)
+		LockPage(rel, 0, ExclusiveLock);
+
 	num_pages = RelationGetNumberOfBlocks(rel);
 
+	if (needLock)
+		UnlockPage(rel, 0, ExclusiveLock);
+
 	/* No point in remembering more than MaxFSMPages pages */
 	maxFreePages = MaxFSMPages;
 	if ((BlockNumber) maxFreePages > num_pages)