Re: [Qemu-devel] [patch v4 05/16] memory: introduce ref, unref interface for MemoryRegionOps

[Jan Kiszka]

On 2012-10-23 14:12, Paolo Bonzini wrote:
> 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?

Once all code that adds/removes memory regions from within access
handlers is converted. Legacy is biting, not necessarily the pure model.

>  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.

Jan

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