Re: Bug#139792: emacs21: Press PageDown, get infinite loop

[Rob Browning]

I've verified that this bug still exists in the current Debian Emacs
21.2 package.

Thanks

Nick <nick@nickwillson.com> writes:

> Package: emacs21
> Version: 21.1-7
> Severity: normal
>
> The symptom is, visit a buffer with more lines than the frame will
> hold and press PageDown - emacs loops and has to be killed.  I've seen
> this in buffers for text files, dired and info.  It is usually
> sporadic and I have not found it easy to produce a reliable test case,
> I hope the following will serve.  
>
> The problem seems to involve the variable scroll-margin and emacs21.
> I did not have this problem with scroll-margin in emacs20.  It also seems to 
> involve the form of the text in the buffer, e.g. for a text file, not any old 
> text file will show the problem, so I have included text which shows the 
> problem reliably (for me).
>
>
> How to reproduce the problem (probably):
>
>
> 1. Create a file '.emacs' containing the text given in 'Note 1' below.
>
> 2. Create a file 'danger70.txt' containing the text given in 'Note 2'
>    below.
>
> 3. At a bash prompt, give the command "emacs danger70.txt".
>
> 4. You are looking at the file 'danger70.txt' with point in the
>    top left hand corner.
>
> 5. Press PageDown.  Point is on a blank line just below a line
>    containing the text 'your kernel.'.
>
> 6. Press PageDown again.  Emacs becomes unresponsive and consumes 100%
>    CPU.  There are no messages about errors.
>
>
> On my system, emacs reports the PageDown key as follows:
> <next> runs the command scroll-up
> (scroll-up &optional ARG)
>    which is an interactive built-in function.
>
> -- System Information
> Debian Release: 3.0
> Architecture: i386
> Kernel: Linux blackbird 2.2.20 #1 SMP Mon Nov 5 23:13:53 CET 2001 i686
> Locale: LANG=C, LC_CTYPE=en_US
>
> Versions of packages emacs21 depends on:
> ii  dpkg                     1.9.20          Package maintenance system for 
> Deb
> ii  emacsen-common           1.4.15          Common facilities for all 
> emacsen.
> ii  libc6                    2.2.5-3         GNU C Library: Shared libraries 
> an
> ii  libjpeg62                6b-5            The Independent JPEG Group's 
> JPEG 
> ii  liblockfile1             1.03            NFS-safe locking library, 
> includes
> ii  libncurses5              5.2.20020112a-5 Shared libraries for terminal 
> hand
> ii  libpng2                  1.0.12-3        PNG library - runtime
> ii  libtiff3g                3.5.5-6         Tag Image File Format library
> ii  xaw3dg                   1.5-11          Xaw3d widget set
> ii  xlibs                    4.1.0-14        X Window System client libraries
> ii  zlib1g                   1:1.1.4-1       compression library - runtime
>
>
> --- Note 1: text for .emacs
> (custom-set-variables
>   ;; custom-set-variables was added by Custom -- don't edit or cut/paste it!
>   ;; Your init file should contain only one such instance.
>  '(scroll-margin 8))
> (custom-set-faces
>   ;; custom-set-faces was added by Custom -- don't edit or cut/paste it!
>   ;; Your init file should contain only one such instance.
>  )
> --- end of Note 1
>
>
> --- Note 2: text for danger70.txt (copied from a kernel README)
>       Linux kernel release 2.4.xx
>
> These are the release notes for Linux version 2.4.  Read them carefully,
> as they tell you what this is all about, explain how to install the
> kernel, and what to do if something goes wrong. 
>
> WHAT IS LINUX?
>
>   Linux is a Unix clone written from scratch by Linus Torvalds with
>   assistance from a loosely-knit team of hackers across the Net.
>   It aims towards POSIX compliance. 
>
>   It has all the features you would expect in a modern fully-fledged
>   Unix, including true multitasking, virtual memory, shared libraries,
>   demand loading, shared copy-on-write executables, proper memory
>   management and TCP/IP networking. 
>
>   It is distributed under the GNU General Public License - see the
>   accompanying COPYING file for more details. 
>
> ON WHAT HARDWARE DOES IT RUN?
>
>   Linux was first developed for 386/486-based PCs.  These days it also
>   runs on ARMs, DEC Alphas, SUN Sparcs, M68000 machines (like Atari and
>   Amiga), MIPS and PowerPC, and others.
>
> DOCUMENTATION:
>
>  - There is a lot of documentation available both in electronic form on
>    the Internet and in books, both Linux-specific and pertaining to
>    general UNIX questions.  I'd recommend looking into the documentation
>    subdirectories on any Linux FTP site for the LDP (Linux Documentation
>    Project) books.  This README is not meant to be documentation on the
>    system: there are much better sources available.
>
>  - There are various README files in the Documentation/ subdirectory:
>    these typically contain kernel-specific installation notes for some 
>    drivers for example. See ./Documentation/00-INDEX for a list of what
>    is contained in each file.  Please read the Changes file, as it
>    contains information about the problems, which may result by upgrading
>    your kernel.
>
>  - The Documentation/DocBook/ subdirectory contains several guides for
>    kernel developers and users.  These guides can be rendered in a
>    number of formats:  PostScript (.ps), PDF, and HTML, among others.
>    After installation, "make psdocs", "make pdfdocs", or "make htmldocs"
>    will render the documentation in the requested format.
>
> INSTALLING the kernel:
>
>  - If you install the full sources, put the kernel tarball in a
>    directory where you have permissions (eg. your home directory) and
>    unpack it:
>
>               gzip -cd linux-2.4.XX.tar.gz | tar xvf -
>
>    Replace "XX" with the version number of the latest kernel.
>
>    Do NOT use the /usr/src/linux area! This area has a (usually
>    incomplete) set of kernel headers that are used by the library header
>    files.  They should match the library, and not get messed up by
>    whatever the kernel-du-jour happens to be.
>
>  - You can also upgrade between 2.4.xx releases by patching.  Patches are
>    distributed in the traditional gzip and the new bzip2 format.  To
>    install by patching, get all the newer patch files, enter the
>    directory in which you unpacked the kernel source and execute:
>
>               gzip -cd patchXX.gz | patch -p0
>
> --- end of Note 2

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
GPG=1C58 8B2C FB5E 3F64 EA5C  64AE 78FE E5FE F0CB A0AD