touch-packages team mailing list archive

[Michi Henning <michi.henning@xxxxxxxxxxxxx>]

I've spent a lot of hours on this so far, without getting closer :-(

Up front, Timo, if there are shell crashes, that's almost certainly an
unrelated problem. I don't see (even in theory) how a crashing scope
could be responsible for that. For starters, the scope is a separate
unrelated process. When a scope crashes in the middle of executing a
query, the shell eventually gets a "query failed" message. But, in this
case, the scope crashes *after* it has returned from main. The crash is
caused by the C++ runtime clean-up, which uses an atexit handler to
invoke global destructors. So, by the time the telegram scope dies,
whatever queries (if any) have completed already.

As to the crash, I had a look at the code and can't spot anything off-
hand that looks wrong. I also built the scope for the desktop and
tinkered with it. A simple run under valgrind comes up clean. However,
that really doesn't prove anything because, for the scope to do
something interesting, it needs a DB with some data in it, by the looks
of things. So, my test didn't exercise much of the code.

As far as I can see, there no unit tests of any kind for the scope, so
it's difficult to exercise the scope and see whether valgrind comes up
with anything. Michael, I need some help getting the scope to run on the
desktop with representative data so I can instrument it and see whether
something comes up.

I have stared at the unity-scopes code for hours and I can't find
anything that looks fishy. I'm positive that I'm finalising the
boost::log machinery correctly.

For what it's worth, the crash happens when boost::log destroys the
global singleton core instance. (That's a global in boost::log, not in
unity-scopes; there are no globals in unity-scopes.) All of the crashes
are in the exact same place. Basically, core is a class that stores a
pimpl, and the destructor just calls "delete pimpl; pimpl = nullptr;"
The call to delete causes the crash.

The corrupt linked list message is emitted by glib whenever any sort of
memory corruption is detected. This could be a double-free, or it could
be because something has crapped over the heap earlier. It's not
possible to tell with the information we have.

One thing that strikes me is that this crash happens only for the
telegram scope, and we are not seeing it elsewhere. It's got to be
something that is specific to the telegram scope. (This doesn't mean
that the telegram scope is buggy; it could, for example, be caused by
different ordering of global destructors due to the order in which
things are linked.)

There is a similar known issue with boost log due to global destructor
ordering:
http://www.boost.org/doc/libs/1_55_0/libs/log/doc/html/log/rationale/why_crash_on_term.html

However, I don't think this the what's happening to us because, for that
issue, the stack trace should end somewhere inside the locale conversion
code.

One thought: I could put together a PPA with a hacked-up registry that
sets MALLOC_CHECK_=2 just for the telegram scope when it is run. The
hope is that this might give us a crash that's more informative. We
could even release with this hack. After all, the scope is crashing as
is; if we are lucky, it'll crash a little sooner.

-- 
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to unity-scope-mediascanner
in Ubuntu.
https://bugs.launchpad.net/bugs/1472755

Title:
  corrupted double-linked list probably cause by telegram scope

Status in Canonical System Image:
  Triaged
Status in libqtelegram package in Ubuntu:
  Triaged
Status in unity-scope-mediascanner package in Ubuntu:
  Invalid
Status in unity-scopes-api package in Ubuntu:
  Invalid

Bug description:
  The Ubuntu Error Tracker has been receiving reports about a problem
  regarding unity-scope-mediascanner.  This problem was most recently
  seen with version 1.7.16, the problem page at
  https://errors.ubuntu.com/problem/21d9e7ddf91a26b21abfb2758315ad41fcfd3fa9
  contains more details.

  "/usr/lib/arm-linux-gnueabihf/unity-scopes/scoperunner:*** Error in
  `/usr/lib/arm-linux-gnueabihf/unity-scopes/scoperunner': corrupted
  double-linked list: ADDR ***"

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