Re: Lockup

[Jan Djärv]

YAMAMOTO Mitsuharu skrev:
> > > > > > On Thu, 10 Aug 2006 08:20:24 +0200, Jan Djärv <address@hidden> said:
>
> > > Hi, I just had a lockup occuring.  Here is a backtrace:
>
> > I've checked in a fix, but I beleive the race condition still exists
> > on multiprocessor machines.  I can't see a way to fix that except
> > move to SYNC_INPUT.
>
> Maybe I'm missing something, but doesn't adding BLOCK_INPUT around
> closedir (and opendir) help?

In this particular case it would help, but in general the problem is that the 
signal handler gets called when the main thread is executing in the mutex code 
(pthread_mutex_unlock).  Later when the signal handler tries to get the mutex, 
it locks up, it is actually not allowed to call mutex functions from a signal 
handler.  The mutex is there to protect from other (Gnome) threads that also 
call malloc/free.

But if a Gnome thread has the mutex and before it has blocked signals, the 
signal handler is run in parallell on another processor, there will be 
problems.  If we move to SYNC_INPUT there will be no malloc/free called in the 
signal handler and we only need the mutex to hamdle concurrent access.

        Jan D.


> > #22 0x080cac12 in XTread_socket (sd=0, expected=1, hold_quit=0xbfabf5ac)
> >     at /home/tmp/emacs/src/xterm.c:7067
> > #23 0x080f90dc in read_avail_input (expected=1)
> >     at /home/tmp/emacs/src/keyboard.c:6737
> > #24 0x080f9283 in handle_async_input () at /home/tmp/emacs/src/keyboard.c:6883
> > #25 0x080f9317 in input_available_signal (signo=29)
> >     at /home/tmp/emacs/src/keyboard.c:6925
> > #26 <signal handler called>
> > #27 0xb795d27d in pthread_mutex_unlock ()
> >    from /lib/tls/i686/cmov/libpthread.so.0
> > #28 0xb77a62f5 in free () from /lib/tls/i686/cmov/libc.so.6
> > #29 0xb77caa08 in closedir () from /lib/tls/i686/cmov/libc.so.6
> > #30 0x08122c57 in directory_files_internal_unwind (dh=161026626)
> >     at /home/tmp/emacs/src/dired.c:137