Re: a race condition between rsrv_init() and casStatsFetch()

["Kim, Kukhee via Core-talk" <core-talk@aps.anl.gov>]

Hi Michael,

You are right. 

It is a false alarm. A guard code has been added before calling casStatsFetch().

Somehow, we are using way behind one in SLAC.

Thank you

Best regards,

Kukhee

--------------------------------------------

Kukhee Kim

TID AIR Advanced Control System

SLAC National Accelerator Laboratory

2575 Sand Hill Rd, MS 94

Menlo Park, CA 94025

Email: khkim@SLAC.Stanford.EDU

Phone: (650)926-4912

Fax:   (650)926-2923

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From: Michael Davidsaver <mdavidsaver@gmail.com>
Sent: Wednesday, September 18, 2019 5:52 PM
To: Kim, Kukhee <khkim@slac.stanford.edu>
Cc: EPICS Core-Talk <core-talk@aps.anl.gov>
Subject: Re: a race condition between rsrv_init() and casStatsFetch()

 

Is this issue distinct from what was fixed with https://github.com/epics-modules/iocStats/pull/21

On Wed, Sep 18, 2019, 4:14 PM Kim, Kukhee via Core-talk <core-talk@aps.anl.gov> wrote:

Hi Everyone,

Some of our colleagues in SLAC found a race condition between rsrv_init() and casStatsFetch() during starting iocs. iocAdmin calls casStatsFetch() periodically to get CA statistics. The casStatsFetch relies on a global mutex clientQlock which is created by rsrv_init(). 

We found that the casStatsFetch is called before the rsrv_init is completed during iocs start, sometimes.

We would like to add the following code into veery first part of casStatsFetch function as a protection to avoid trouble.

if(!clientQlock) {

    return;

}

One of function in caservertask.c, casr() has the protection as above, but the casStatsFetch does not have it.

I think epics 3.15, 3.16, and epics 7 all of them have the same potential issue.

Thank you for your concern.

Best regards,

Kukhee

--------------------------------------------

Kukhee Kim

TID AIR Advanced Control System

SLAC National Accelerator Laboratory

2575 Sand Hill Rd, MS 94

Menlo Park, CA 94025

Email: khkim@SLAC.Stanford.EDU

Phone: (650)926-4912

Fax:   (650)926-2923