cfs: fix interaction of 'vacuum full', 'drop table' and cfs_gc.

Author: Sokolov Yura

src/backend/storage/smgr/md.c

@@ -451,6 +451,7 @@ mdcreate(SMgrRelation reln, ForkNumber forkNum, bool isRedo)
 void
 mdunlink(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo)
 {
+	bool cfs_gc_locked = false;
 	/*
 	 * We have to clean out any pending fsync requests for the doomed
 	 * relation, else the next mdsync() will fail.  There can't be any such
@@ -461,14 +462,33 @@ mdunlink(RelFileNodeBackend rnode, ForkNumber forkNum, bool isRedo)
 	if (!RelFileNodeBackendIsTemp(rnode))
 		ForgetRelationFsyncRequests(rnode.node, forkNum);
 
-	/* Now do the per-fork work */
-	if (forkNum == InvalidForkNumber)
+	if (md_use_compression(rnode, forkNum == InvalidForkNumber ? MAIN_FORKNUM : forkNum))
 	{
-		for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
+		cfs_gc_locked = true;
+		cfs_control_gc_lock();
+	}
+
+	PG_TRY();
+	{
+		/* Now do the per-fork work */
+		if (forkNum == InvalidForkNumber)
+		{
+			for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
+				mdunlinkfork(rnode, forkNum, isRedo);
+		}
+		else
 			mdunlinkfork(rnode, forkNum, isRedo);
+		}
 	}
-	else
-		mdunlinkfork(rnode, forkNum, isRedo);
+	PG_CATCH();
+	{
+		if (cfs_gc_locked)
+			cfs_control_gc_unlock();
+		PG_RE_THROW();
+	}
+	PG_END_TRY();
+	if (cfs_gc_locked)
+		cfs_control_gc_unlock();
 }
 
 static void