Subject: bug#31771: 26.1; Writing image file with emacs hangs entire system

From: Noam Postavsky <[email-masked]>
Date: Sat, 09 Jun 2018 15:47:27 -0400

tags 31771 + unreproducible
quit

Adam <[email-masked]> writes:

> After following these commands, your emacs should freeze, and then your
> entire system should hang a few seconds later.

I couldn't reproduce this.  No hang, and if I look closely, I can see
the one black pixel rendered correctly in the top left corner.

Is your whole system completely frozen, or is it perhaps just using so
much RAM that it goes into swap and starts thrashing and becomes very
slow?  If the former, I guess it's some kind of graphics driver thing,
though it seems a bit funny that an image as simple as a single black
pixel could wreck it.

> My hunch: this is caused by emacs trying to render the image after it's
> saved. Unfortunately, this causes emacs and my system to hang, so I
> can't provide any core dumps. I'm using linux 4.16.13, mesa 18.1.1,
> libpng 1.6.34, and imagemagick 7.0.7.38

> Configured features:
> XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
> ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
> GTK3 X11 MODULES THREADS LIBSYSTEMD LCMS2

Do you really have imagemagick 7?  Or do maybe also have imagemagic 6?
As far as I know, the patch for Emacs to use v7 is not merged yet:
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25967#41