s3: Add a "lock_order" argument to db_open

This will be used to enforce a lock hierarchy between the databases. We have
seen deadlocks between locking.tdb, brlock.tdb, serverid.tdb and notify*.tdb.
These should be fixed by refusing a dbwrap_fetch_locked that does not follow a
defined lock hierarchy.

3 files changed, 26 insertions, 3 deletions

diff --git a/source3/lib/dbwrap/dbwrap_open.c b/source3/lib/dbwrap/dbwrap_open.c
index 6b8be2de16..23d299511b 100644
--- a/source3/lib/dbwrap/dbwrap_open.c
+++ b/source3/lib/dbwrap/dbwrap_open.c
@@ -62,11 +62,26 @@ bool db_is_local(const char *name)
 struct db_context *db_open(TALLOC_CTX *mem_ctx,
 			   const char *name,
 			   int hash_size, int tdb_flags,
-			   int open_flags, mode_t mode)
+			   int open_flags, mode_t mode,
+			   enum dbwrap_lock_order lock_order)
 {
 	struct db_context *result = NULL;
 #ifdef CLUSTER_SUPPORT
-	const char *sockname = lp_ctdbd_socket();
+	const char *sockname;
+#endif
+
+	if ((lock_order != DBWRAP_LOCK_ORDER_1) &&
+	    (lock_order != DBWRAP_LOCK_ORDER_2)) {
+		/*
+		 * Only allow 2 levels. ctdb gives us 3, and we will
+		 * have the watchers database soon.
+		 */
+		errno = EINVAL;
+		return NULL;
+	}
+
+#ifdef CLUSTER_SUPPORT
+	sockname = lp_ctdbd_socket();
 
 	if(!sockname || !*sockname) {
 		sockname = CTDB_PATH;
diff --git a/source3/lib/dbwrap/dbwrap_open.h b/source3/lib/dbwrap/dbwrap_open.h
index 5a172a4a2a..2763ef2ade 100644
--- a/source3/lib/dbwrap/dbwrap_open.h
+++ b/source3/lib/dbwrap/dbwrap_open.h
@@ -29,6 +29,11 @@ struct db_context;
  */
 bool db_is_local(const char *name);
 
+enum dbwrap_lock_order {
+	DBWRAP_LOCK_ORDER_1 = 1,
+	DBWRAP_LOCK_ORDER_2 = 2
+};
+
 /**
  * Convenience function that will determine whether to
  * open a tdb database via the tdb backend or via the ctdb
@@ -38,6 +43,7 @@ bool db_is_local(const char *name);
 struct db_context *db_open(TALLOC_CTX *mem_ctx,
 			   const char *name,
 			   int hash_size, int tdb_flags,
-			   int open_flags, mode_t mode);
+			   int open_flags, mode_t mode,
+			   enum dbwrap_lock_order lock_order);
 
 #endif /* __DBWRAP_OPEN_H__ */
diff --git a/source3/lib/dbwrap/dbwrap_private.h b/source3/lib/dbwrap/dbwrap_private.h
index 4806618543..d0b3279368 100644
--- a/source3/lib/dbwrap/dbwrap_private.h
+++ b/source3/lib/dbwrap/dbwrap_private.h
@@ -23,6 +23,8 @@
 #ifndef __DBWRAP_PRIVATE_H__
 #define __DBWRAP_PRIVATE_H__
 
+#include "dbwrap/dbwrap_open.h"
+
 struct db_record {
 	TDB_DATA key, value;
 	NTSTATUS (*store)(struct db_record *rec, TDB_DATA data, int flag);