Management Console freezes when connecting/disconnecting modem sites

Issue:
Management Console freezes when attempting to connect or disconnect a modem site.

Product Line:
ION Enterprise 6.0.x
StruxureWare Power Monitoring 7.0.x
Power Monitoring Expert 7.2.x

Environment:
Management Console Configuration

Cause:

• When the ION/SPM/PME software is installed on any of Microsoft’s 64 bit operating systems (Windows 7 64bit, Windows 2008 Server 64bit, and Windows 2008 R2 Server) with multiple modems connected, a com port can get in a locked state.
• When this happens, siteserv freezes which in turn stops the connection schedule from trying to connect to other sites. Data cannot be downloaded from any modem sites from that point forward until the problem is noticed and the server is rebooted. When siteserv.exe freezes, it cannot be killed by any means except a complete server reboot.
• The above scenario is what happens when a lockup occurs on the native com port (COM1). When a lockup happens on an expanded comport, siteserv and the connection schedule freeze but will recover after 10 to 20 minutes depending on the type of com port expansion hardware/driver being used.
• Root Cause: Siteserv sends a call to a Microsoft API to open a com port in exclusive mode. The request is handled and the comport gets locked to the siteserv process. When siteserv is finished and wants to hang up the modem, it sends a CloseHandle() call the API but no response is returned. The com port remains blocked by the OS and siteserv is waiting for a response that never occurs.
• Explanation from the Microsoft developer:  The issue is a mismatch between the number of times LowerRTSTimer timer is queued and the number of times it is associated timer DPC (PerhapsLowerRTSDpc) runs. This happens because KeSetTimer doesn’t cancel already queued timer DPC and a DPC can be queued in only one DPC queue at a given time. If the timer fires when a timer DPC from a previous timer is already queued we’ll run into this and have pending CountOfTryingToLowerRTS and DpcCount.

Resolution:
A validation of the final publicly released Microsoft patch (kb 2809097) has been completed in the lab where it has successfully resolved lockups on both expanded and native serial com ports. The patch should be applied to all ION Enterprise, SPM, or PME systems where the OS is 64 bit and modems are utilized.

The hotfix can be downloaded from the following link.

https://support.microsoft.com/en-us/kb/2809097

Note: The siteserv lockup behavior has not been observed on systems running PME 8.0

Publicado para: Schneider Electric Portugal