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Date: Tue, 23 Aug 2011 13:41:48 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v4 2/5] ramlist mutex
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To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Umesh Deshpande <udeshpan@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org, quintela@redhat.com

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