[AGENT++] Double free ... (memory corruption)

[Frank Fock]

Hi Jens,

This is indeed most likely a synchronization problem.
Please make sure that you follow the AGENT++ locking
concept as follows:

First lock the whole MIB with

mib->lock_mib();

//now you can make registration changes or lookup
an MibEntry to modify (or just read).

// when you got the pointer to the entry to modify
// lock it with:
mib_entry->start_sync();

// now you may unlock the MIB
mib->unlock_mib();

// modify the mib_entry
...

// unlock it
mib_entry->end_sync();


Within the MibTable::update() method, you must not lock
the Mib, because MibTable::update() will be called only
by AGENT++ if the Mib has been locked. Nevertheless,
you will need to lock the entry itself within the
update method, if you modify the entry itself.

Hope this helps.

Best regards,
Frank


On 26.10.2010 10:04, Jens Rehsack wrote:
> Hi all,
>
> I received during a long-term test a memory corruption:
>
> *** glibc detected *** ./src/smart-snmpd: double free or corruption
> (fasttop): 0xb3d00f68 ***
> ======= Backtrace: =========
> /lib/tls/i686/cmov/libc.so.6(+0x6b591)[0x5b2591]
> /lib/tls/i686/cmov/libc.so.6(+0x6cde8)[0x5b3de8]
> /lib/tls/i686/cmov/libc.so.6(cfree+0x6d)[0x5b6ecd]
> /usr/lib/libstdc++.so.6(_ZdlPv+0x21)[0x44e741]
> /sysmgmt/opt/smart-snmp/lib/libagent++.so.35(_ZN7Agentpp21OidxPtrEntryPtrAVLMap3delEPNS_4OidxE+0x6d)[0xe1676d]
> /sysmgmt/opt/smart-snmp/lib/libagent++.so.35(_ZN7Agentpp8MibTableD0Ev+0x1e1)[0xe26ce1]
> ./src/smart-snmpd[0x807c7c8]
> ./src/smart-snmpd[0x807ad12]
> ./src/smart-snmpd[0x8080439]
> /sysmgmt/opt/smart-snmp/lib/libagent++.so.35(_ZN7Agentpp14thread_starterEPv+0xbd)[0xe69d1d]
> /lib/tls/i686/cmov/libpthread.so.0(+0x596e)[0x93596e]
> /lib/tls/i686/cmov/libc.so.6(clone+0x5e)[0x614a4e]
>
> Using objdump I could guess the source location:
> include/agent_pp/List.h:829 - looks for me (quick look)
> as a threading issue (is the access to _need_rebalancing locked? I
> didn't find where ...)
>
> Wouldn't it reasonable to use member variables? Or much better: std::map<>?
>
> /Jens
> _______________________________________________
> AGENTPP mailing list
> AGENTPP at agentpp.org
> http://lists.agentpp.org/mailman/listinfo/agentpp

-- 
AGENT++
http://www.agentpp.com
http://www.snmp4j.com
http://www.mibexplorer.com
http://www.mibdesigner.com