Re: [Qemu-devel] [PATCH v4 13/13] block/mirror: Block "device IO" during mirror exit

[Fam Zheng <famz@redhat.com>]

On Tue, 05/19 10:04, Paolo Bonzini wrote:
> On 19/05/2015 13:49, Fam Zheng wrote:
> > When block job mirror is finished, the source and target is synced. But
> > we call bdrv_swap() later in main loop bh. If the guest write before
> > that, target will not get the new data.
> 
> This is too late.  As a rule, the blocker must be established before
> calling bdrv_drain, and removed on the next yield (in this case, before
> the assignment to last_pause_ns).

I don't understand. If the blocker is removed before mirror_run returns,
wouldn't more device IO already hit source image by the time mirror_exit runs?

Fam

> 
> Paolo
> 
> > Reported-by: Wen Congyang <wency@cn.fujitsu.com>
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  block/mirror.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/block/mirror.c b/block/mirror.c
> > index 58f391a..d96403b 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -320,6 +320,8 @@ static void mirror_drain(MirrorBlockJob *s)
> >  
> >  typedef struct {
> >      int ret;
> > +    /* Use to pause device IO during mirror exit */
> > +    Error *blocker;
> >  } MirrorExitData;
> >  
> >  static void mirror_exit(BlockJob *job, void *opaque)
> > @@ -328,6 +330,8 @@ static void mirror_exit(BlockJob *job, void *opaque)
> >      MirrorExitData *data = opaque;
> >      AioContext *replace_aio_context = NULL;
> >  
> > +    bdrv_op_unblock(s->common.bs, BLOCK_OP_TYPE_DEVICE_IO, data->blocker);
> > +    error_free(data->blocker);
> >      if (s->to_replace) {
> >          replace_aio_context = bdrv_get_aio_context(s->to_replace);
> >          aio_context_acquire(replace_aio_context);
> > @@ -563,8 +567,10 @@ immediate_exit:
> >      bdrv_release_dirty_bitmap(bs, s->dirty_bitmap);
> >      bdrv_iostatus_disable(s->target);
> >  
> > -    data = g_malloc(sizeof(*data));
> > +    data = g_malloc0(sizeof(*data));
> >      data->ret = ret;
> > +    error_setg(&data->blocker, "mirror job exiting");
> > +    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, data->blocker);
> >      block_job_defer_to_main_loop(&s->common, mirror_exit, data);
> >  }
> >  
> >