Re: [PATCH v2 04/17] xen/cpupool: switch cpupool id to unsigned

[Jürgen Groß <jgross@xxxxxxxx>]

On 01.12.20 09:55, Jan Beulich wrote:
> On 01.12.2020 09:21, Juergen Gross wrote:
> > @@ -243,11 +243,11 @@ void cpupool_put(struct cpupool *pool)
> >    * - unknown scheduler
> >    */
> >   static struct cpupool *cpupool_create(
> > -    int poolid, unsigned int sched_id, int *perr)
> > +    unsigned int poolid, unsigned int sched_id, int *perr)
> >   {
> >       struct cpupool *c;
> >       struct cpupool **q;
> > -    int last = 0;
> > +    unsigned int last = 0;
> >   
> >       *perr = -ENOMEM;
> >       if ( (c = alloc_cpupool_struct()) == NULL )
> > @@ -256,7 +256,7 @@ static struct cpupool *cpupool_create(
> >       /* One reference for caller, one reference for cpupool_destroy(). */
> >       atomic_set(&c->refcnt, 2);
> >   
> > -    debugtrace_printk("cpupool_create(pool=%d,sched=%u)\n", poolid, sched_id);
> > +    debugtrace_printk("cpupool_create(pool=%u,sched=%u)\n", poolid, sched_id);
> >   
> >       spin_lock(&cpupool_lock);
> Below from here we have
>
>      c->cpupool_id = (poolid == CPUPOOLID_NONE) ? (last + 1) : poolid;
>
> which I think can (a) wrap to zero and (b) cause a pool with id
> CPUPOOLID_NONE to be created. The former is bad in any event, and
> the latter will cause confusion at least with cpupool_add_domain()
> and cpupool_get_id(). I realize this is a tangential problem, i.e.
> may want fixing in a separate change.
Yes, this is an issue today already, and it is fixed in patch 5.

> > --- a/xen/common/sched/private.h
> > +++ b/xen/common/sched/private.h
> > @@ -505,8 +505,8 @@ static inline void sched_unit_unpause(const struct 
> > sched_unit *unit)
> >   
> >   struct cpupool
> >   {
> > -    int              cpupool_id;
> > -#define CPUPOOLID_NONE    (-1)
> > +    unsigned int     cpupool_id;
> > +#define CPUPOOLID_NONE    (~0U)
> How about using XEN_SYSCTL_CPUPOOL_PAR_ANY here? Furthermore,
> together with the remark above, I think you also want to consider
> the case of sizeof(unsigned int) > sizeof(uint32_t).
With patch 5 this should be completely fine.


Juergen

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