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Date: Tue, 23 Aug 2011 09:16:30 -0300
From: Marcelo Tosatti <mtosatti@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v4 2/5] ramlist mutex
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Umesh Deshpande <udeshpan@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org, quintela@redhat.com

On Tue, Aug 23, 2011 at 01:41:48PM +0200, Paolo Bonzini wrote:
> On 08/23/2011 11:17 AM, Marcelo Tosatti wrote:
> >>>>  >    typedef struct RAMList {
> >>>>  >  +    QemuMutex mutex;
> >>>>  >        uint8_t *phys_dirty;
> >>>>  >        QLIST_HEAD(ram, RAMBlock) blocks;
> >>>>  >        QLIST_HEAD(, RAMBlock) blocks_mru;
> >>>
> >>>  A comment on what the mutex protects would be good.
> 
> Indeed, especially because Umesh wanted to use the ramlist+iothread
> combo as a rw-lock: iothread = read-lock for the I/O thread, ramlist
> = read-lock for the migration thread, together = exclusive (write)
> lock. But I think I talked him out of this. :)  It's not a bad idea
> in general, it just sounds like overkill in this case.
> 
> >And on the lock ordering.
> 
> I think when only two locks are involved, we can always assume
> iothread is outer and the other is inner.  Do you agree?
> 
> Paolo

Yep.