[AGENT++] Potential deadlocks for SNMP Subagents ...

[Frank Fock]

Hi Jens,

I do not think that (1) would cause any deadlock, because Mib::find_next
is only called when mib->lock() is acquired.

Thanks for reporting (2) it has been fixed by AgentX++v1.4.12b.

Best regards,
Frank

Jens Engel wrote:

>APPLIES-TO: SNMP Subagents (connected via AgentX)
>IN:  file:agentx_subagent.cpp (AgentX++ v1.4.11)
>NOTE: Problematic lines marked with "XXX".
>
>1. SubAgentXMib::find_next(): If logging is more verbose (DEADLOCK OCCURs):
>
>int SubAgentXMib::find_next(MibContext* context, const Oidx& oid,
>MibEntryPtr& entry, Request* req, const int reqind)
>{
>      int err = Mib::find_next(context, oid, entry, req, reqind);
>      if (err == SNMP_ERROR_SUCCESS) {
>            ...
>            // test for valid range
>            if (range.get_lower() <= range.get_upper()) {
>                  if (!is_complex_node(entry)) {
>                    if (!range.includes(*entry->key()))
>                        return sNMP_SYNTAX_NOSUCHOBJECT;
>                  }
>                  else {
>                          LOG_BEGIN(DEBUG_LOG | 3);
>                    LOG("SubAgentXMib: find next
>(lower)(upper)(incl)(succ)");
>                    LOG(range.get_lower().get_printable());
>                    LOG(range.get_upper().get_printable());
>                    LOG((range.is_lower_included()) ? "TRUE":"FALSE");
>XXX                 // XXX-JE-PATCH: NO; find_succ locks thread => deadlock
>!!
>XXX                 // LOG(entry->find_succ(oid, req).get_printable());
>                    LOG_END;
>
>2. In process_response(): Missing queue->unlock()??? (by Inspection)
>
>void SubAgentXMib::process_response(AgentXRequest* r)
>{
>      ...
>      queue->lock();
>      ...
>      if (!pending) {
>            ...
>XXX         queue->unlock();  //< XXX-JE-PATCH: Is this not missing here
>(before return)???
>            return;
>     ...
>}
>
>Jens Engel, EG/FW-BTC4, Marconi Communications GmbH.
>Tel. ++49 7191 13-4702
>mailto:Jens.Engel at marconi.com
>
>
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>