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Date: Tue, 23 Oct 2012 14:12:10 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [patch v4 05/16] memory: introduce ref,
	unref interface for MemoryRegionOps
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Liu Ping Fan <pingfank@linux.vnet.ibm.com>, Stefan Hajnoczi <stefanha@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Avi Kivity <avi@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>

Il 23/10/2012 14:04, Jan Kiszka ha scritto:
>>> >>
>>> >> So the stop_machine idea is thrown away?  
>> > 
>> > IIRC I convinced myself that it's just as bad.
> One tricky part with stop machine is that legacy code may trigger it
> while holding the BQL, does not expect to lose that lock even for a
> brief while, but synchronizing on other threads does require dropping
> the lock right now. Maybe an implementation detail, but at least a nasty
> one.

But it would only be triggered by hot-unplug, no?  That is already an
asynchronous action, so it is not a problem to delay the actual
stop_machine+qdev_free (and just that part!) to a bottom half or another
place when it is safe to drop the BQL.

Paolo