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

[Marcelo Tosatti]

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.