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

From: "Jürgen Groß" <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: George Dunlap <george.dunlap@citrix.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <iwj@xenproject.org>, Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 04/17] xen/cpupool: switch cpupool id to unsigned
Date: Tue, 1 Dec 2020 10:01:01 +0100	[thread overview]
Message-ID: <eed1baac-a6eb-f10b-7272-742c08f5124e@suse.com> (raw)
In-Reply-To: <a0bac022-fe6e-aae6-6d07-6a2b9bc492b3@suse.com>

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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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