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Date: Tue, 25 Jun 2013 09:53:52 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 0/3] make bh safe with hot-unplug
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To: liu ping fan <qemulist@gmail.com>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Il 25/06/2013 08:32, liu ping fan ha scritto:
> On Tue, Jun 25, 2013 at 2:24 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 25/06/2013 19:38, Liu Ping Fan ha scritto:
>>> This series relies on refcnt of object used by bh callback to run against unplug.
>>>
>>> Open issue:
>>> Another choice may be rcu, but I think some issues are hard to resolve.
>>> Using rcu, we have two choice:
>>>   when holding object refcnt, call qemu_bh_delete(); then after grace period, we can release.
>>>   Or making qemu_bh_delete() sync in the path of DeviceState's finalization.
>>
>> What do you mean exactly?  qemu_bh_delete() is async, but it operates on
>> dynamically-allocated memory.
>>
> Before DeviceState is freed, we should make sure the bh is delete, and
> not related bh is in fly.

The bh need not be deleted.  It just needs to be not-scheduled (easy,
qemu_bh_delete does that) and not running.

The latter part could be the hard one in a multi-threaded context, but I
think it's up to the device to ensure it.  It doesn't _have_ to be hard.
 For example, joining the data-plane thread would do that as well.

Paolo

>> Paolo
>>
>>> but currently, the callers of qemu_bh_delete() can not satisfy any of the two condition.
>>