Re: [Xen-devel] [PATCH v4 5/7] libxl: support unmapping static shared memory areas during domain destruction

[Julien Grall <julien.grall@xxxxxxx>]

On 12/02/18 15:17, Zhongze Liu wrote:
> Hi Julien,
Hi,

> 2018-02-12 23:09 GMT+08:00 Julien Grall <julien.grall@xxxxxxx>:
> > Hi,
> >
> > On 12/02/18 14:52, Zhongze Liu wrote:
> > > 2018-02-08 0:54 GMT+08:00 Julien Grall <julien.grall@xxxxxxx>:
> > > > On 07/02/18 16:27, Zhongze Liu wrote:
> > > It seems that I mistakenly use transaction as a global lock. Now I don't
> > > have
> > > any reasons not putting the unmap out of the transaction, but this will
> > > break
> > > the original transaction into two, and I do think that we need some
> > > explicit
> > > locking here.
> >
> > Can you explain why you need specific locking here? What are you trying to
> > protect? Are you trying to protect against two process doing the unmap?
> Yes.
I don't think you have to worry about the locking here. With the current 
interface, the regions cannot be modified after the guest has booted. So 
the addresses will always stay valid.
This code path should never be called concurrently, as a lot of code in 
libxl, so I think someone else will take care about that for you (I will 
let Wei confirm here).
In any case, the worst that could happen is the unmap is called twice on 
the same region. So you would get spurious error message. Not that bad.
Cheers,

--
Julien Grall

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