Re: [Qemu-devel] [PATCH 2/3] COLO: Shutdown related socket fd while do failover

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Hailiang Zhang (zhang.zhanghailiang@huawei.com) wrote:
> On 2017/1/18 19:01, Dr. David Alan Gilbert wrote:
> > * zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> > > If the net connection between primary host and secondary host breaks
> > > while COLO/COLO incoming threads are doing read() or write().
> > > It will block until connection is timeout, and the failover process
> > > will be blocked because of it.
> > > 
> > > So it is necessary to shutdown all the socket fds used by COLO
> > > to avoid this situation. Besides, we should close the corresponding
> > > file descriptors after failvoer BH shutdown them,
> > > Or there will be an error.
> > 
> > Hi,
> >    There are two parts to this patch:
> >     a) Add some semaphores to sequence failover
> >     b) Use shutdown()
> > 
> >    At first I wondered if perhaps they should be split; but I see
> > the reason for the semaphores is mostly to stop the race between
> > the fd's getting closed and the shutdown() calls; so I think it's
> > OK.
> > 
> 
> Hi,
> 
> Yes, you are right, maybe i should add some comments about that.
> Will do in next version.
> 
> > Do you have any problems with these semaphores during powering off the
> > guest?
> > 
> 
> No, we didn't encounter any problems or trigger any bugs in our test
> with this semaphores. In what places do you doubt it may has problems ? :)

I just wondered about other exit cases other than failover; e.g. what
if the guest shutdown or something like that, would it get stuck
waiting for the colo_incoming_sem.

Dave

> Thanks,
> Hailiang
> 
> > Dave
> > 
> > 
> > 
> > 
> > > Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> > > Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> > > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > ---
> > >   include/migration/migration.h |  3 +++
> > >   migration/colo.c              | 43 +++++++++++++++++++++++++++++++++++++++++++
> > >   2 files changed, 46 insertions(+)
> > > 
> > > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > > index 487ac1e..7cac877 100644
> > > --- a/include/migration/migration.h
> > > +++ b/include/migration/migration.h
> > > @@ -113,6 +113,7 @@ struct MigrationIncomingState {
> > >       QemuThread colo_incoming_thread;
> > >       /* The coroutine we should enter (back) after failover */
> > >       Coroutine *migration_incoming_co;
> > > +    QemuSemaphore colo_incoming_sem;
> > > 
> > >       /* See savevm.c */
> > >       LoadStateEntry_Head loadvm_handlers;
> > > @@ -182,6 +183,8 @@ struct MigrationState
> > >       QSIMPLEQ_HEAD(src_page_requests, MigrationSrcPageRequest) src_page_requests;
> > >       /* The RAMBlock used in the last src_page_request */
> > >       RAMBlock *last_req_rb;
> > > +    /* The semaphore is used to notify COLO thread that failover is finished */
> > > +    QemuSemaphore colo_exit_sem;
> > > 
> > >       /* The semaphore is used to notify COLO thread to do checkpoint */
> > >       QemuSemaphore colo_checkpoint_sem;
> > > diff --git a/migration/colo.c b/migration/colo.c
> > > index 08b2e46..3222812 100644
> > > --- a/migration/colo.c
> > > +++ b/migration/colo.c
> > > @@ -59,6 +59,18 @@ static void secondary_vm_do_failover(void)
> > >           /* recover runstate to normal migration finish state */
> > >           autostart = true;
> > >       }
> > > +    /*
> > > +     * Make sure COLO incoming thread not block in recv or send,
> > > +     * If mis->from_src_file and mis->to_src_file use the same fd,
> > > +     * The second shutdown() will return -1, we ignore this value,
> > > +     * It is harmless.
> > > +     */
> > > +    if (mis->from_src_file) {
> > > +        qemu_file_shutdown(mis->from_src_file);
> > > +    }
> > > +    if (mis->to_src_file) {
> > > +        qemu_file_shutdown(mis->to_src_file);
> > > +    }
> > > 
> > >       old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
> > >                                      FAILOVER_STATUS_COMPLETED);
> > > @@ -67,6 +79,8 @@ static void secondary_vm_do_failover(void)
> > >                        "secondary VM", FailoverStatus_lookup[old_state]);
> > >           return;
> > >       }
> > > +    /* Notify COLO incoming thread that failover work is finished */
> > > +    qemu_sem_post(&mis->colo_incoming_sem);
> > >       /* For Secondary VM, jump to incoming co */
> > >       if (mis->migration_incoming_co) {
> > >           qemu_coroutine_enter(mis->migration_incoming_co);
> > > @@ -81,6 +95,18 @@ static void primary_vm_do_failover(void)
> > >       migrate_set_state(&s->state, MIGRATION_STATUS_COLO,
> > >                         MIGRATION_STATUS_COMPLETED);
> > > 
> > > +    /*
> > > +     * Wake up COLO thread which may blocked in recv() or send(),
> > > +     * The s->rp_state.from_dst_file and s->to_dst_file may use the
> > > +     * same fd, but we still shutdown the fd for twice, it is harmless.
> > > +     */
> > > +    if (s->to_dst_file) {
> > > +        qemu_file_shutdown(s->to_dst_file);
> > > +    }
> > > +    if (s->rp_state.from_dst_file) {
> > > +        qemu_file_shutdown(s->rp_state.from_dst_file);
> > > +    }
> > > +
> > >       old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
> > >                                      FAILOVER_STATUS_COMPLETED);
> > >       if (old_state != FAILOVER_STATUS_ACTIVE) {
> > > @@ -88,6 +114,8 @@ static void primary_vm_do_failover(void)
> > >                        FailoverStatus_lookup[old_state]);
> > >           return;
> > >       }
> > > +    /* Notify COLO thread that failover work is finished */
> > > +    qemu_sem_post(&s->colo_exit_sem);
> > >   }
> > > 
> > >   void colo_do_failover(MigrationState *s)
> > > @@ -361,6 +389,14 @@ out:
> > > 
> > >       timer_del(s->colo_delay_timer);
> > > 
> > > +    /* Hope this not to be too long to wait here */
> > > +    qemu_sem_wait(&s->colo_exit_sem);
> > > +    qemu_sem_destroy(&s->colo_exit_sem);
> > > +    /*
> > > +     * Must be called after failover BH is completed,
> > > +     * Or the failover BH may shutdown the wrong fd that
> > > +     * re-used by other threads after we release here.
> > > +     */
> > >       if (s->rp_state.from_dst_file) {
> > >           qemu_fclose(s->rp_state.from_dst_file);
> > >       }
> > > @@ -385,6 +421,7 @@ void migrate_start_colo_process(MigrationState *s)
> > >       s->colo_delay_timer =  timer_new_ms(QEMU_CLOCK_HOST,
> > >                                   colo_checkpoint_notify, s);
> > > 
> > > +    qemu_sem_init(&s->colo_exit_sem, 0);
> > >       migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
> > >                         MIGRATION_STATUS_COLO);
> > >       colo_process_checkpoint(s);
> > > @@ -423,6 +460,8 @@ void *colo_process_incoming_thread(void *opaque)
> > >       uint64_t value;
> > >       Error *local_err = NULL;
> > > 
> > > +    qemu_sem_init(&mis->colo_incoming_sem, 0);
> > > +
> > >       migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
> > >                         MIGRATION_STATUS_COLO);
> > > 
> > > @@ -533,6 +572,10 @@ out:
> > >           qemu_fclose(fb);
> > >       }
> > > 
> > > +    /* Hope this not to be too long to loop here */
> > > +    qemu_sem_wait(&mis->colo_incoming_sem);
> > > +    qemu_sem_destroy(&mis->colo_incoming_sem);
> > > +    /* Must be called after failover BH is completed */
> > >       if (mis->to_src_file) {
> > >           qemu_fclose(mis->to_src_file);
> > >       }
> > > --
> > > 1.8.3.1
> > > 
> > > 
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> > 
> > .
> > 
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK