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

[Paolo Bonzini <pbonzini@redhat.com>]

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