Add memory barriers to ensure write/read order of TLI and LSN

Author: dAdAbird

contrib/pg_tde/src/access/pg_tde_xlog_smgr.c

@@ -88,7 +88,14 @@ TDEXLogGetEncKeyLsn()
 static void
 TDEXLogSetEncKeyLocation(WALLocation loc)
 {
+	/* 
+	 * Write TLI first and then LSN. The barrier ensures writes won't be
+	 * reordered. When reading, the opposite must be done (with a matching
+	 * barrier in between), so we always see a valid TLI after observing a
+	 * valid LSN. 
+	 */
 	pg_atomic_write_u32(&EncryptionState->enc_key_tli, loc.tli);
+	pg_write_barrier();
 	pg_atomic_write_u64(&EncryptionState->enc_key_lsn, loc.lsn);
 }
 
@@ -353,7 +360,12 @@ tdeheap_xlog_seg_read(int fd, void *buf, size_t count, off_t offset,
 		keys = pg_tde_fetch_wal_keys(start);
 	}
 
+	/* 
+	 * The barrier ensures that we always read a vaild TLI after the valid LSN.
+	 * See the comment in TDEXLogSetEncKeyLocation()
+	 */
 	write_key_lsn = TDEXLogGetEncKeyLsn();
+	pg_read_barrier();
 
 	if (!XLogRecPtrIsInvalid(write_key_lsn))
 	{

contrib/pg_tde/src/include/pg_tde_fe.h

@@ -88,6 +88,8 @@ static int	tde_fe_error_level = 0;
 #define FreeFile(file) fclose(file)
 
 #define pg_fsync(fd) fsync(fd)
+
+#define pg_read_barrier() NULL
 #endif							/* FRONTEND */
 
 #endif							/* PG_TDE_EREPORT_H */