Re: CVS commit: src/sys/arch/xen/xen

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On 15.05.2011 21:11, Mindaugas Rasiukevicius wrote:
> This is not correct.  Atomic op might decrease the reference count to
> 1 while other thread executes xbdi_put() before xbdi_refcnt is fetched,
> thus decreasing it to 0.  In such case, both threads would fetch 0.
> 
> The following is a correct way:
> 
>       if (atomic_dec_uint_nv(&xbdip->xbdi_refcnt) == 0)
>               xbdback_finish_disconnect(xbdip);
> 
> Also, it seems there is no need for xbdi_refcnt to be volatile.

Good point; I was pondering about the _nv() version when I made the
change, but forgot about the possible concurrency regarding refcnt fetch
(not actually possible as port-xen is not MP, but will become soonish)

I'll remove the volatile declaration too, only xbdi_put/_get use the
refcnt for G/C anyway.

Thanks for pointing that out!

-- 
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost