Re: [Xen-devel] [PATCH v4 21/23] xen/vpl011: buffer out chars when the backend is xen

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 20 Oct 2018, Julien Grall wrote:
> Hi Stefano,
> 
> On 10/20/18 12:20 AM, Stefano Stabellini wrote:
> > On Mon, 8 Oct 2018, Jan Beulich wrote:
> > > > > > On 05.10.18 at 20:47, <sstabellini@xxxxxxxxxx> wrote:
> > > > --- a/xen/drivers/char/console.c
> > > > +++ b/xen/drivers/char/console.c
> > > > @@ -406,6 +406,13 @@ static void dump_console_ring_key(unsigned char
> > > > key)
> > > >    */
> > > >   static unsigned int __read_mostly console_rx = 0;
> > > >   +struct domain *console_input_domain(void)
> > > > +{
> > > > +    if ( console_rx == 0 )
> > > > +            return NULL;
> > > > +    return get_domain_by_id(console_rx - 1);
> > > 
> > > This acquires a domain reference, yet I can't see that reference
> > > getting dropped anywhere in the caller.
> > 
> > Well spotted!
> > 
> > I'll add a comment here as a reminder, and I'll drop the domain
> > reference in the caller (xen/arch/arm/vpl011.c:vpl011_write_data_xen).
> 
> Why do you use get_domain_by_id() and not rcu_lock_domain_by_id()? The latter
> is recommend for short live reference.

Yes, you are right, that is a better solution. I'll change it to use
rcu_lock_domain_by_id. We still need the corresponding rcu_unlock_domain
call, so I'll still add a new comment and the corresponding unlock call.

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