Re: [PATCH v2 19/23] migration/multifd: Cleanup multifd_save_cleanup()

[Peter Xu <peterx@redhat.com>]

On Fri, Feb 02, 2024 at 05:54:23PM -0300, Fabiano Rosas wrote:
> peterx@redhat.com writes:
> 
> > From: Peter Xu <peterx@redhat.com>
> >
> > Shrink the function by moving relevant works into helpers: move the thread
> > join()s into multifd_send_terminate_threads(), then create two more helpers
> > to cover channel/state cleanups.
> >
> > Add a TODO entry for the thread terminate process because p->running is
> > still buggy.  We need to fix it at some point but not yet covered.
> >
> > Suggested-by: Fabiano Rosas <farosas@suse.de>
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> 
> Reviewed-by: Fabiano Rosas <farosas@suse.de>
> 
> minor comment below
> 
> > ---
> >  migration/multifd.c | 91 +++++++++++++++++++++++++++++----------------
> >  1 file changed, 59 insertions(+), 32 deletions(-)
> >
> > diff --git a/migration/multifd.c b/migration/multifd.c
> > index 4ab8e6eff2..4cb0d2cc17 100644
> > --- a/migration/multifd.c
> > +++ b/migration/multifd.c
> > @@ -593,6 +593,11 @@ static void multifd_send_terminate_threads(void)
> >       * always set it.
> >       */
> >      qatomic_set(&multifd_send_state->exiting, 1);
> > +
> > +    /*
> > +     * Firstly, kick all threads out; no matter whether they are just idle,
> > +     * or blocked in an IO system call.
> > +     */
> >      for (i = 0; i < migrate_multifd_channels(); i++) {
> >          MultiFDSendParams *p = &multifd_send_state->params[i];
> >  
> > @@ -601,6 +606,21 @@ static void multifd_send_terminate_threads(void)
> >              qio_channel_shutdown(p->c, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
> >          }
> >      }
> > +
> > +    /*
> > +     * Finally recycle all the threads.
> > +     *
> > +     * TODO: p->running is still buggy, e.g. we can reach here without the
> > +     * corresponding multifd_new_send_channel_async() get invoked yet,
> > +     * then a new thread can even be created after this function returns.
> > +     */
> 
> Series on the list:
> 
> https://lore.kernel.org/r/20240202191128.1901-1-farosas@suse.de

Thanks a lot.  I'll read it later today.

> 
> > +    for (i = 0; i < migrate_multifd_channels(); i++) {
> > +        MultiFDSendParams *p = &multifd_send_state->params[i];
> > +
> > +        if (p->running) {
> > +            qemu_thread_join(&p->thread);
> > +        }
> > +    }
> >  }
> >  
> >  static int multifd_send_channel_destroy(QIOChannel *send)
> > @@ -608,6 +628,41 @@ static int multifd_send_channel_destroy(QIOChannel *send)
> >      return socket_send_channel_destroy(send);
> >  }
> >  
> > +static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
> > +{
> > +    if (p->registered_yank) {
> > +        migration_ioc_unregister_yank(p->c);
> > +    }
> > +    multifd_send_channel_destroy(p->c);
> > +    p->c = NULL;
> > +    qemu_mutex_destroy(&p->mutex);
> > +    qemu_sem_destroy(&p->sem);
> > +    qemu_sem_destroy(&p->sem_sync);
> > +    g_free(p->name);
> > +    p->name = NULL;
> > +    multifd_pages_clear(p->pages);
> > +    p->pages = NULL;
> > +    p->packet_len = 0;
> > +    g_free(p->packet);
> > +    p->packet = NULL;
> > +    g_free(p->iov);
> > +    p->iov = NULL;
> > +    multifd_send_state->ops->send_cleanup(p, errp);
> > +
> > +    return *errp == NULL;
> 
> I think technically this would require the ERRP_GUARD() macro?

I normally only use ERRP_GUARD() if there can be any caller passing in
NULL, or when I am not sure it's always !NULL.

What I wanted to add here is actually assert(errp), but then I noticed
*errp==NULL plays the same role as that, because if errp==NULL, it'll crash
here when dereferencing, so it actually has an implicit assert(errp);
exactly what I wanted, but even one line less (even if not obvious).

-- 
Peter Xu