Weird rawhide desktop behavior

[Jonathan Corbet]

Here's a strange pathology that just bit me for the first time in a while,
though I've seen it before.  I'm not sure where to file a bug on this
one...

In short: I'll be working away, minding my own business, when the desktop
goes completely dead - no response to any key or mouse events.  That said,
the X server is still running; the pointer still moves with the mouse.  I
can also switch to another virtual console with alt-ctrl-Fn.  Sometimes
things start working again after some time (measured in minutes);
sometimes I lose patience and start over.  Today I went and made lunch and
it never came back.

I've tried killing off applications to see if somebody has some sort of
all-inclusive grab, but I can't find the right one if that's the case.  I
can kill something like Firefox and verify that the process is gone, but
the Firefox window remains on-screen when I return to X.

For a while I could reliably cause this by hitting the audio mute button
on my keyboard, but that went away just when I was about to take a moment
and write a note like this.  When it hit me today, I was scrolling a
LibreOffice window with the scrollwheel.

Anybody got a clue what's going on, or where I could look to get more
information?

Thanks,

jon