Unpack struct vecheader

The bitset packing of the resign_lsb and heap_index in struct vecheader
was causing a race condition, since both bindrdataset and heap
operations tried to access the same byte (even though they are accessing
different fields).

While heap operations are protected by the node lock of the header being
inserted, they aren't protected by the node locks of the headers being
displaced, leading to the race condition.

This commit fixes the issue by reverting the struct packing
optimization.

diff --git a/lib/dns/include/dns/rdatavec.h b/lib/dns/include/dns/rdatavec.h
index f7ba2e1a26f89b099f48a6a073f9092d493f88d0..b92f6762740db36b7f9a32427be30a10cbdc0263 100644 (file)
--- a/lib/dns/include/dns/rdatavec.h
+++ b/lib/dns/include/dns/rdatavec.h
@@ -81,18 +81,24 @@ struct dns_vecheader {
        _Atomic(uint16_t)    attributes;
        _Atomic(dns_trust_t) trust;
 
+       /*%
+        * Locked by the heap lock. Can't be packed together with other fields
+        * since it is protected by a different lock.
+        */
+       unsigned int heap_index;
+
        /*%
         * Locked by the owning node's lock.
         */
-       uint16_t       resign_lsb : 1;
-       unsigned int   heap_index : 31;
        uint32_t       serial;
        dns_ttl_t      ttl;
        dns_typepair_t typepair;
 
-       /* resigning (zone). The lsb is not adjacent for struct packing reasons
+       /*
+        * resigning (zone).
         */
        isc_stdtime_t resign;
+       uint16_t      resign_lsb : 1;
 
        /*%
         * Link to the other versions of this rdataset.