Re: [Qemu-devel] [RFC PATCH v4 2/5] ramlist mutex

[Paolo Bonzini]

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