Re: [Qemu-devel] [PATCH RFC v6 6/7] migration: fix some error handling

[Fei Li]

On 10/31/2018 03:49 AM, Dr. David Alan Gilbert wrote:
> * Fei Li (address@hidden) wrote:
> > Add error handling for qemu_ram_foreach_migratable_block() when
> > it fails.
> >
> > Always call migrate_set_error() to set the error state without relying
> > on whether multifd_save_cleanup() succeeds. As the passed &local_err
> > is never used in multifd_save_cleanup(), remove it.
> >
> > Signed-off-by: Fei Li <address@hidden>
> > ---
> >   migration/migration.c    | 5 +----
> >   migration/postcopy-ram.c | 3 +++
> >   migration/ram.c          | 7 +++----
> >   migration/ram.h          | 2 +-
> >   4 files changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 87dfc7374f..3b8b7ab4f9 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1377,7 +1377,6 @@ static void migrate_fd_cleanup(void *opaque)
> >       qemu_savevm_state_cleanup();
> >   
> >       if (s->to_dst_file) {
> > -        Error *local_err = NULL;
> >           QEMUFile *tmp;
> >   
> >           trace_migrate_fd_cleanup();
> > @@ -1388,9 +1387,7 @@ static void migrate_fd_cleanup(void *opaque)
> >           }
> >           qemu_mutex_lock_iothread();
> >   
> > -        if (multifd_save_cleanup(&local_err) != 0) {
> > -            error_report_err(local_err);
> > -        }
> > +        multifd_save_cleanup();
> >           qemu_mutex_lock(&s->qemu_file_lock);
> >           tmp = s->to_dst_file;
> >           s->to_dst_file = NULL;
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index e5c02a32c5..4ca2bc02b3 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -1117,6 +1117,9 @@ int postcopy_ram_enable_notify(MigrationIncomingState 
> > *mis)
> >   
> >       /* Mark so that we get notified of accesses to unwritten areas */
> >       if (qemu_ram_foreach_migratable_block(ram_block_enable_notify, mis)) {
> > +        error_report("ram_block_enable_notify failed");
> > +        close(mis->userfault_event_fd);
> > +        close(mis->userfault_fd);
> I don't think these close() calls are safe.  This code is just after
> starting the fault thread, and the fault thread has a poll() call on
> these fd's, so we can't close them until we've instructed that thread
> to exit.
>
> We should fall out through postcopy_ram_incoming_cleanup, and because
> the thread exists it should do a notify to the thread, a join and then
> only later do the close calls.
>
> Dave
I see the postcopy_ram_incoming_cleanup() already include the
notify & join the fault thread & close these two fds and other more cleanup,
thus that means directly replace the above two close() with
postcopy_ram_incoming_cleanup() is ok, right? :)

BTW, does the parameter "&local_err" for multifd_save_cleanup(&local_err) is
reserved for some reason? As I notice no code is using this error parameter,
and if it is reserved for nothing I'd like to delete it just as the 
second paragraph
of the commit message said. :)

Have a nice day, thanks
Fei
> >           return -1;
> >       }
> >   
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 8f03afe228..57cb1bee3d 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -922,7 +922,7 @@ static void multifd_send_terminate_threads(Error *err)
> >       }
> >   }
> >   
> > -int multifd_save_cleanup(Error **errp)
> > +int multifd_save_cleanup(void)
> >   {
> >       int i;
> >       int ret = 0;
> > @@ -1082,9 +1082,8 @@ static void multifd_new_send_channel_async(QIOTask *task, 
> > gpointer opaque)
> >   
> >       if (qio_task_propagate_error(task, &local_err)) {
> >           migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
> > -        if (multifd_save_cleanup(&local_err) != 0) {
> > -            migrate_set_error(migrate_get_current(), local_err);
> > -        }
> > +        multifd_save_cleanup();
> > +        migrate_set_error(migrate_get_current(), local_err);
> >       } else {
> >           p->c = QIO_CHANNEL(sioc);
> >           qio_channel_set_delay(p->c, false);
> > diff --git a/migration/ram.h b/migration/ram.h
> > index 046d3074be..0d1215209e 100644
> > --- a/migration/ram.h
> > +++ b/migration/ram.h
> > @@ -43,7 +43,7 @@ uint64_t ram_bytes_remaining(void);
> >   uint64_t ram_bytes_total(void);
> >   
> >   int multifd_save_setup(void);
> > -int multifd_save_cleanup(Error **errp);
> > +int multifd_save_cleanup(void);
> >   int multifd_load_setup(void);
> >   int multifd_load_cleanup(Error **errp);
> >   bool multifd_recv_all_channels_created(void);
> > --
> > 2.13.7
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK