On Mon, Jul 04, 2016 at 06:43:42PM +0200, Marc-André Lureau wrote: > Hi > > On Mon, Jul 4, 2016 at 6:31 PM, Daniel P. Berrange <berra...@redhat.com> > wrote: > > On Mon, Jul 04, 2016 at 05:38:23PM +0200, marcandre.lur...@redhat.com wrote: > >> From: Marc-André Lureau <marcandre.lur...@redhat.com> > >> > >> It turns out qemu is calling exit() in various places from various > >> threads without taking much care of resources state. The atexit() > >> cleanup handlers cannot easily destroy resources that are in use (by > >> the same thread or other). > > > > [snip] > > > >> Instead of using a atexit() handler, only run the chardev cleanup as > >> initially proposed at the end of main(), where there are less chances > >> (hic) of conflicts or other races. > > > > This doesn't really seem all that much safer. There's still plenty of > > chance that threads are running in the background at the end of the > > main() method, so plenty of scope for the qemu_chr_cleanup() call to > > cause threads to segv by destroying the chardevs they're using behind > > their back. > > Yep yep > > Note, just before the end of main() all CPU threads should be frozen. > > Is there any reason why there is no support for joining an cleaning up > all the running threads at this point? > > > IIUC, the original intent here was that we call unlink() on the UNIX > > socket paths when QEMU exits. > > > > Surely we can come up with a way to that, and only that, upon exit, > > without actually having to free the chardev memory with all the risks > > that entails. > > Doesn't sound that simple if you can't take the lock. And when you do > you can't destroy it. It sounds hard to avoid races, so I might be > missing something.
The other option is to not try to do this at the chardev level at all. Instead we could have the QIOChannelSocket impl maintain a list of UNIX socket paths that need unlinking, and have it register an atexit() handler itself, whose sole purpose is to unlink the paths. We could simply have a global GList of char* UNIX socket paths, so the atexit handler would not touch the QIOChannelSocket objects at all. This avoiding all races or issues with concurrent access. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
