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

[Paolo Bonzini]

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