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Date: Fri, 16 Jan 2015 16:03:40 +0300
From: Vladimir Sementsov-Ogievskiy <vsementsov@parallels.com>
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Subject: Re: [Qemu-devel] [PATCH 7/9] block-migration: remove not needed
	iothread lock
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To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, den@openvz.org, jsnow@redhat.com, stefanha@redhat.com


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.