Re: [Xen-devel] [PATCH] Avoid panic when adjusting sedf parameters

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 11/17/2011 02:48 PM, Keir Fraser wrote:
> On 17/11/2011 13:30, "Jan Beulich"<JBeulich@xxxxxxxx>  wrote:
>
> > > +#define for_each_domain_in_cpupool(_d,_c)       \
> > > + for ( (_d) = rcu_dereference(domain_list);     \
> > > +       (_d) != NULL;                            \
> > > +       (_d) = rcu_dereference((_d)->next_in_list )) \
> > Wouldn't this, up to here, simply be for_each_domain()?
> >
> > > +       if ((_d)->cpupool == (_c))
> > This is dangerous - consider code like
> I also wonder (and this is true for the existing open-coded versions too)
> whether we have sufficient locking around use of d->cpupool? Do these loops
> hold enough locks to ensure that d->cpupool doesn't change under their feet?
d->cpupool is changed in three functions:

I was just preparing a patch for cpupool_unassign_cpu() which is lacking
rcu_lock_domain().
cpupool_add_domain() is called only for domains not yet in the domain list.
sched_move_domain() is only called with domain lock held.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
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