wish (and gitk) crashes when window is closed

[Stephen Warren]

When the user closes the window that wish displays (e.g. types CTRL+F4 in XFCE), wish experiences a segfault. This can be reproduced either by simply running "wish", or by running a wish-based application such as gitk.

$ gdb wish
GNU gdb (Ubuntu 7.11-0ubuntu1) 7.11
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from wish...(no debugging symbols found)...done.
(gdb) r
Starting program: /usr/bin/wish
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
% [New Thread 0x7ffff3d1e700 (LWP 25046)]

<< Give wish window focus, type CTRL+F4 >>

Thread 1 "wish" received signal SIGSEGV, Segmentation fault.
__lll_unlock_elision (lock=0x7ffff7a7b900 <notifierMutex>, private=0) at ../sysdeps/unix/sysv/linux/x86/elision-unlock.c:29
29 ../sysdeps/unix/sysv/linux/x86/elision-unlock.c: No such file or directory.
(gdb) bt
#0 __lll_unlock_elision (lock=0x7ffff7a7b900 <notifierMutex>, private=0) at ../sysdeps/unix/sysv/linux/x86/elision-unlock.c:29
#1 0x00007ffff6039cd8 in pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:94
#2 0x00007ffff780f0f7 in Tcl_FinalizeNotifier () from /usr/lib/x86_64-linux-gnu/libtcl8.6.so
#3 0x00007ffff77cec5d in ?? () from /usr/lib/x86_64-linux-gnu/libtcl8.6.so
#4 0x00007ffff7792549 in ?? () from /usr/lib/x86_64-linux-gnu/libtcl8.6.so
#5 0x00007ffff7792346 in Tcl_Exit () from /usr/lib/x86_64-linux-gnu/libtcl8.6.so
#6 0x00007ffff7acf0e0 in Tk_MainEx () from /usr/lib/x86_64-linux-gnu/libtk8.6.so
#7 0x000000000040094c in ?? ()
#8 0x00007ffff7323a00 in __libc_start_main (main=0x400920, argc=1, argv=0x7fffffffe2f8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>,
    stack_end=0x7fffffffe2e8) at libc-start.c:289
#9 0x0000000000400989 in _start ()

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: tk 8.6.0+9
ProcVersionSignature: Ubuntu 4.4.0-13.29-generic 4.4.5
Uname: Linux 4.4.0-13-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_modeset nvidia
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Mar 16 22:51:17 2016
InstallationDate: Installed on 2016-03-03 (14 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160122.2)
SourcePackage: tcltk-defaults
UpgradeStatus: No upgrade log present (probably fresh install)

[Stephen Warren (srwarren)]

The same issue happens when running:
gdb --args wish /usr/bin/gitk -- -n 100
(or just "gitk -n 100" if not running under gdb)

The same issue repros when closing the window in the following ways:
- Clicking the close "x" icon on the window title bar
- Selecting close from the window's menu (in XFCE the button in the top-left of the window title bar)
- In gitk, selecting File -> Close