qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: A bug of Monitor Chardev ?


From: Daniel P . Berrangé
Subject: Re: A bug of Monitor Chardev ?
Date: Tue, 8 Jun 2021 16:37:11 +0100
User-agent: Mutt/2.0.7 (2021-05-04)

On Tue, Jun 08, 2021 at 04:07:30PM +0200, Markus Armbruster wrote:
> "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)"
> <longpeng2@huawei.com> writes:
> 
> > We find a race during QEMU starting, which would case the QEMU process 
> > coredump.
> >
> > <main loop>                             |    <MON iothread>
> >                                         |
> > [1] create MON chardev                  |
> > qemu_create_early_backends              |
> >   chardev_init_func                     |
> >                                         |
> > [2] create MON iothread                 |
> > qemu_create_late_backends               |
> >   mon_init_func                         |
> >     aio_bh_schedule-----------------------> monitor_qmp_setup_handlers_bh
> > [3] enter main loog                     |    tcp_chr_update_read_handler
> > (* A client come in, e.g. Libvirt *)    |      update_ioc_handlers
> > tcp_chr_new_client                      |
> >   update_ioc_handlers                   |
> >                                         |
> >     [4] create new hup_source           |
> >         s->hup_source = *PTR1*          |
> >           g_source_attach(s->hup_source)|
> >                                         |        [5] 
> > remove_hup_source(*PTR1*)
> >                                         |            (create new hup_source)
> >                                         |             s->hup_source = *PTR2*
> >         [6] g_source_attach_unlocked    |
> >               *PTR1* is freed by [5]    |
> >                     
> > Do you have any suggestion to fix this bug ? Thanks!
> 
> Do we?  We talked, but I'm not sure we reached a conclusion.

Seems like we ended up with two options.

  1. A workaround for the current  specific problem by rearranging
     the initilization code in the monitor a little.

  2. A design fix of splitting the chardev creation into two
     parts, one creation, and one activation.

The latter is significantly more work, but is a better long term bet IMHO.
But what we really is someone motivated to actually implement one of the
two options.

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|




reply via email to

[Prev in Thread] Current Thread [Next in Thread]