#307 segfault in task with bad vars and/or position file

[Sebastian Kuzminsky]

Gene Haskett reported the bug here: http://thread.gmane.org/gmane.linux.distributions.emc.devel/8656/

Master branch, realtime build, task would segfault at startup.

Gene found a work-around here:

http://thread.gmane.org/gmane.linux.distributions.emc.devel/8656/focus=8678

The position.txt file was empty. He removed both the position.txt file and the vars file (linuxcnc.vars), and the segfault went away and everything worked fine.

[Sebastian Kuzminsky]

This can be reproduced in sim:

build master
start the axis.ini config, let axis start, then quit
truncate the position.txt file to 0 bytes
restart axis.ini, milltask dumps core, preventing linuxcnc from starting

I think there are two problems here:

The first bug is that milltask segfaults when it tries to read a 0-byte position.txt file.

The other bug is that the position.txt file can be corrupted (the original bug was apparently preceded by linuxcnc crashing). We should be using the rename(2) method to provide safe, atomic updates of all our critical files.

[Michael Haberler]

Gene - I think the meaningless backtrace came about because gdb was not installed

please 'sudo apt-get install gdb'

this should enable a meaningful backtrace on segfaults

-m

[Sebastian Kuzminsky]

bug is also present in 2.5

[Gene Heskett]

On Monday 04 November 2013 03:08:35 Sebastian Kuzminsky did opine:

• Group: --> 2.5.next

---

[bugs:#307] segfault in task with bad vars and/or position file

Status: open
Labels: Task Controller
Created: Mon Dec 17, 2012 04:29 PM UTC by Sebastian Kuzminsky
Last Updated: Mon Dec 17, 2012 04:29 PM UTC
Owner: nobody

Gene Haskett reported the bug here:
http://thread.gmane.org/gmane.linux.distributions.emc.devel/8656/

Master branch, realtime build, task would segfault at startup.

Gene found a work-around here:

http://thread.gmane.org/gmane.linux.distributions.emc.devel/8656/focus=8
678

The position.txt file was empty. He removed both the position.txt file
and the vars file (linuxcnc.vars), and the segfault went away and
everything worked fine.

And I still have to do that from time to time. The atom box on the lathe
can crash while exiting lcnc (so can the box I run the mill with, but not
near as often, supposedly identical ARK brand shoeboxes purchased about a
year apart from the same dealer in Texas) and either will leave empty files
about once in 5 or 6 crashes.

Unforch, when they do hang mid-exit, both requiring a reset button restart,
they leave no clues in the logs, absolutely zip, not a character.

Else I would have been posting it every time it happened.

Cheers, Gene

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)

There's just something I don't like about Virginia; the state.
A pen in the hand of this president is far more
dangerous than 200 million guns in the hands of
law-abiding citizens.

[Chris Radek]

In 2.5 with a zero-byte position.txt file, I get a failed startup (with no segfault) but also it heals: it writes a new and valid position.txt file.

I'm reassigning this to the 2.6 group.

[Gene Heskett]

On Thursday 17 April 2014 12:04:46 Chris Radek did opine:

• Group: 2.5.next --> 2.6
• Comment:

In 2.5 with a zero-byte position.txt file, I get a failed startup (with
no segfault) but also it heals: it writes a new and valid position.txt
file.

I'm reassigning this to the 2.6 group.

---

[bugs:#307] segfault in task with bad vars and/or position file

Status: open
Group: 2.6
Labels: Task Controller
Created: Mon Dec 17, 2012 04:29 PM UTC by Sebastian Kuzminsky
Last Updated: Mon Nov 04, 2013 04:42 AM UTC
Owner: nobody

Gene Haskett reported the bug here:
http://thread.gmane.org/gmane.linux.distributions.emc.devel/8656/

Master branch, realtime build, task would segfault at startup.

Gene found a work-around here:

http://thread.gmane.org/gmane.linux.distributions.emc.devel/8656/focus=8
678

The position.txt file was empty. He removed both the position.txt file
and the vars file (linuxcnc.vars), and the segfault went away and
everything worked fine.

First, its Heskett, and I haven't had any problem with that that I can
recall in quite a while. OTOH, I am on the 2.5.3 branch ATM since about
that time frame too.

But here is a small clue: I get a blast of 8 or 10 lines of errors in the
terminal screen I run it from IF I use the windows close button. I do not
get that, getting a completely clean shutdown, if I use the file menus quit
button.

Cheers, Gene

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page http://geneslinuxbox.net:6309/gene
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS