freeze due to interrupted futex system calls

[Jose Antonio Ortega Ruiz]

Symptoms:

The symptoms are that emacs freezes: it does not respond to any
keystroke and all frames are blank. 'top' reports that the process is
stopped (status 'S') and using 'strace -p' I get repeatedly the
following trace:

  futex(0x407d9860, FUTEX_WAIT, 2, NULL)  = -1 EINTR (Interrupted system call)
  --- SIGIO (I/O possible) @ 0 (0) ---
  sigreturn()                             = ? (mask now [SEGV])

The freeze happens intermittently (once a day or so; i use emacs most
of the time) and i haven't found a way of reproducing it. It seems to
happen always when switching open frames using the window manager.
Most of the time, i have separate emacs frames for eshell, emacs-w3m,
erc and gnus, but the freeze also happened with just two frames
(eshell and a visited text file).

The bug also happens in emacs 23.3.1 with the same frequency, but in
emacs 21.3.50.1 compiled with gtk2.0 it's much more frequent (maybe
once every hour).

Futexes seem to be a new low-level synchronisation primitive of 2.6
linux kernels, used to build mutexes, semaphores and the like.

In GNU Emacs 21.3.50.1 (i386-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2004-08-23 on imladris, modified by Debian
configured using `configure '--build' 'i386-linux' '--host' 'i386-linux' 
'--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' 
'--localstatedir=/var' '--infodir=/usr/share/info' '--mandir=/usr/share/man' 
'--with-pop=yes' '--with-gif' '--with-x=yes' '--with-x-toolkit=athena' 
'--with-toolkit-scroll-bars' 'CFLAGS=-DDEBIAN -g -O2' 'build_alias=i386-linux' 
'host_alias=i386-linux''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: nil
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Major mode: VHDL/es

Minor modes in effect:
  display-time-mode: t
  erc-services-mode: t
  erc-notify-mode: t
  erc-autojoin-mode: t
  erc-button-mode: t
  erc-ring-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-match-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-netsplit-mode: t
  recentf-mode: t
  auto-image-file-mode: t
  partial-completion-mode: t
  global-auto-revert-mode: t
  auto-compression-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  column-number-mode: t
  line-number-mode: t

Recent input:
k e d SPC b y SPC " SPC <backspace> s i g n a l s SPC 
o r SPC o t h e r SPC s p u r i o u s SPC w a k e u 
p s " ) <backspace> . . . SPC n o t SPC t h a t SPC 
i SPC c a n SPC m a k e SPC m u c h SPC s e n s e SPC 
o f SPC i t SPC : ( <switch-frame> M-x r e p o r <tab> 
b <tab> <return>

Recent messages:
nntp-handle-authinfo: Process nntpd<1> not running
Auto-saving...
Mark saved where search started [3 times]
Mark set [2 times]
Undo!
Message modified; kill anyway? (y or n) 
Mark set [2 times]
Auto-saving...done
Auto-saving...done
Loading emacsbug...done