Re: [Qemu-devel] [PATCH 7/9] block-migration: remove not needed iothread lock

[Vladimir Sementsov-Ogievskiy]

Best regards,
Vladimir

On 09.01.2015 01:28, Paolo Bonzini wrote:
> On 11/12/2014 15:17, Vladimir Sementsov-Ogievskiy wrote:
> > -    qemu_mutex_lock_iothread();
> > +    bdrv_reset_dirty_bitmap(bs, bmds->dirty_bitmap, cur_sector, nr_sectors);
> > +
> >       blk->aiocb = bdrv_aio_readv(bs, cur_sector, &blk->qiov,
> >                                   nr_sectors, blk_mig_read_cb, blk);
> >   
> > -    bdrv_reset_dirty_bitmap(bs, bmds->dirty_bitmap, cur_sector, nr_sectors);
> > -    qemu_mutex_unlock_iothread();
> > -
> bdrv_aio_readv is not thread safe, so it needs the iothread lock.
>
> bdrv_reset_dirty_bitmap is also not thread safe, because
> bmds->dirty_bitmap is accessed concurrently by bdrv_reset_dirty
> (discard) and bdrv_set_dirty (write).  So it needs the iothread lock too.
>
> Moving bdrv_reset_dirty_bitmap before the read is a good idea.
>
> Paolo
Ok.