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<== Date ==> <== Thread ==>

Subject: Re: Possible bug in ca_clear_channel
From: Benjamin Franksen <benjamin.franksen@helmholtz-berlin.de>
To: EPICS Core-Talk <tech-talk@aps.anl.gov>
Date: Tue, 6 Jan 2015 11:51:19 +0100
Hi Everyone,

thanks to Michael it is clear now that the bug is in the sequencer, not
in ca_clear_channel. Sorry for the false alarm.

I'll fix this in both the 2.1 and the 2.2 branch and will make releases
for both ASAP.

Cheers
Ben

On Monday 05 January 2015 12:33:40 Michael Davidsaver wrote:
> In the stack trace you send I see a clear deadlock between threads 2
> and 3 when shutting down a CA subscription.
>
> Thread 2 has entered seq_mon_handler() and is attempting to lock
> programLock.
>
> However thread 3 holds programLock while calling ca_clear_channel,
> which (now) blocks until the event queue is clear.  The last bit was
> to fix bug #1179642.
>
> I think this would best if the sequencer was changed to unlock around
> calls to ca_clear_channel().
>
> https://bugs.launchpad.net/epics-base/+bug/1179642
>
> On 01/05/2015 08:01 AM, Benjamin Franksen wrote:
> > Thanks Michael
> >
> > I am now testing on my machine at work (32 bits, 4 cores) instead of
> > my home machine (64 bits, 2 cores) and cannot reproduce the failure
> > with the reassign test. Instead I get a hanging test for
> > pvAssignStress.t (which executes "./pvAssignStress -S -t -d
> > ../pvAssignStress.db" i.e. this is a test where state machine and
> > database are on the same IOC). I have compiled against
> > base-3.14.12.4. Again, the hangup is inside ca_clear_channel as can
> > be easily seen from the stack trace (look at Thread 3), see the
> > attached gdb output.
> >
> > I'll send you the corresponding output on my home machine when I get
> > back from work.
> >
> > Cheers
> > Ben
> >
> > On Monday 29 December 2014 16:26:30 you wrote:
> >> On 12/29/2014 03:05 PM, Benjamin Franksen wrote:
> >> ...
> >>
> >>> I have been using gdb for analyzing core dumps before but I have
> >>> no
> >>> idea how to get a stack trace from a living (well, deadlocked)
> >>> program.
> >>
> >> As you would run "gdb execname corefile" you can also run "gdb
> >> execname pid#".
> >>
> >> Once attached run "thread apply all backtrace" which will produce a
> >> lot of output.  Copy this to a file and email to me.  There is
> >> probably a way to pipe to file, but I can't remember atm.
> >>
> >>> Furthermore,
> >>> ddd has been broken for some time now on the machine I am
> >>> currently
> >>> at and I am not very familiar with the CLI. So, if you could give
> >>> me instructions on what commands I am supposed to use... I know
> >>> "bt" for stack trace but that is the limit of my knowledge about
> >>> the CLI.
> >>
> >> To expand on "bt" remember "thr app all bt".
> >
> > --
> > "Make it so they have to reboot after every typo." ― Scott Adams
> >
> > ________________________________
> >
> > Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
> >
> > Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher
> > Forschungszentren e.V.
> >
> > Aufsichtsrat: Vorsitzender Prof. Dr. Dr. h.c. mult. Joachim Treusch,
> > stv. Vorsitzende Dr. Beatrix Vierkorn-Rudolph Geschäftsführung:
> > Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking
> >
> > Sitz Berlin, AG Charlottenburg, 89 HRB 5583
> >
> > Postadresse:
> > Hahn-Meitner-Platz 1
> > D-14109 Berlin
> >
> > http://www.helmholtz-berlin.de

--
"Make it so they have to reboot after every typo." ― Scott Adams

________________________________

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren e.V.

Aufsichtsrat: Vorsitzender Prof. Dr. Dr. h.c. mult. Joachim Treusch, stv. Vorsitzende Dr. Beatrix Vierkorn-Rudolph
Geschäftsführung: Prof. Dr. Anke Rita Kaysser-Pyzalla, Thomas Frederking

Sitz Berlin, AG Charlottenburg, 89 HRB 5583

Postadresse:
Hahn-Meitner-Platz 1
D-14109 Berlin

http://www.helmholtz-berlin.de


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