Fix nesting tdb_traverse in a transaction

Calling tdb_traverse inside a transaction led to the transaction lock being
held indefinitely. This was caused by the tdb_transaction_lock/unlock inside
tdb_traverse: The transaction code holds the global lock at offset
TRANSACTION_LOCK. The call to tdb_transaction_lock does nothing because the
transaction_lock is already being held. tdb_transaction_unlock inside tdb_wrap
resets tdb->have_transaction_lock but does not release the kernel-level fcntl
lock. transaction_commit later on does not release that fcntl lock either,
because tdb->have_transaction_lock was already reset by tdb_transaction().

This patch does fix that problem for me. An alternative would be to make
tdb->have_transaction_lock a counter that can cope with proper nesting, maybe
in other places as well.

Volker
(This used to be commit 89543005fe2e4934b3c560c937d49304a32a7fc2)

1 files changed, 8 insertions, 3 deletions

diff --git a/source4/lib/tdb/common/traverse.c b/source4/lib/tdb/common/traverse.c
index 07b0c23858..5a31742e7b 100644
--- a/source4/lib/tdb/common/traverse.c
+++ b/source4/lib/tdb/common/traverse.c
@@ -232,20 +232,25 @@ int tdb_traverse(struct tdb_context *tdb,
 {
 	struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 	int ret;
+	int in_transaction = (tdb->transaction != NULL);
 
 	if (tdb->read_only || tdb->traverse_read) {
 		return tdb_traverse_read(tdb, fn, private_data);
 	}
 	
-	if (tdb_transaction_lock(tdb, F_WRLCK)) {
-		return -1;
+	if (!in_transaction) {
+		if (tdb_transaction_lock(tdb, F_WRLCK)) {
+			return -1;
+		}
 	}
 
 	tdb->traverse_write++;
 	ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 	tdb->traverse_write--;
 
-	tdb_transaction_unlock(tdb);
+	if (!in_transaction) {
+		tdb_transaction_unlock(tdb);
+	}
 
 	return ret;
 }