RFC: jemalloc: qdbus sigsegv in malloc_init

   Hi,

   the kde team is seeing some strange problems with the new version 
(4.8.1) of devel/dbus-qt4 with current. It does work with stable. I also 
suspect that the problem described below is affecting the experimental 
cinnamon port (an alternative to gnome3, possible replacement of gnome2).

   The problem happens with both i386 and amd64 with empty 
/etc/malloc.conf and simple /etc/make.conf. Everything compiled with 
base gcc (no clang). The kernel was compiled with no debug support, but 
it can enable if needed. There are reports from avilla_at_freebsd.org of 
the same behavior with clang compiled world and kernel and with   
MALLOC_PRODUCTION=yes.

  When qdbus starts, it segfauts. The backtrace of the problem with 
r234769 can be found here: http://pastebin.com/ryBXtqGF. When starting 
the qdbus daemon by hand in a X+twm session, we see it calls calloc many 
times and after a fixed number of times segfaults. We see it segfaults 
at rb_gen (a quite large macro defined at 
$SRC_BASE/contrib/jemalloc/include/jemalloc/internal/rb.h).

  If the daemon is started by hand, I'm able to skip all the calls qdbus 
makes to calloc till the one causing the segfault. At that point, at 
rb_gen, we don't exactly know what is going on or how to debug the 
macro. Ktrace are available, but we were unable to find anything new 
from them.

   With old versions of current before the jemalloc imports (as of March 
30th) the daemon segfaulted at malloc.c:2426. With revisions during 
April 20 to 24th (can be more precise, it was during the jemalloc 
imports) the daemon segfaulted at malloc_init. Bts are available if 
needed, and if necessary I can go back to those revision and recompile 
world+kernel to see its behavior.

   Any help from freebsd-current_at_ (perhaps Jason Evans can help us) will 
be appreciated. Any additional info, like source revisions, can be 
provided. I would like to stress that the experimental devel/dbus-qt4 
works fine with recent stable.