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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.12.2020 10:01, Jürgen Groß wrote:
> 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.

Ah - I didn't expect this kind of fix in a patch with that title,
but yes.

Jan