Re: [PATCH] Avoid panic when adjusting sedf parameters

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 11/17/2011 03:32 PM, Jan Beulich wrote:
>>>> On 17.11.11 at 15:04, Juergen Gross<juergen.gross@ts.fujitsu.com>  wrote:
>> On 11/17/2011 02:52 PM, Keir Fraser wrote:
>>> On 17/11/2011 13:30, "Jan Beulich"<JBeulich@suse.com>   wrote:
>>>
>>>> which would now associate the else with the wrong (inner) if. One
>>>> possible solution that comes to mind would be
>>>>
>>>> #define for_each_domain_in_cpupool(_d,_c) \
>>>>       for_each_domain_in_cpupool (_d) \
>>>>           if ((_d)->cpupool != (_c)) \
>>>>               continue; \
>>>>           else
>>>>
>>>> but I think I had seen a more clever solution to this problem, but cannot
>>>> remember/locate it right now.
>>> Given the gcc ({}) construction, you could do a double-loop:
>>>    for ( (_d) = rcu_dereference(domain_list);     \
>>>          (_d) != NULL;                            \
>>>          ({ while ((_d) = rcu_dereference((_d)->next_in_list != NULL)
>>>                if ((_d)->cpupool == (_c)) break;
>>>             (_d); }) )
>>>
>>> A bit ugly. ;-) And I still worry about cpupool locking...
>> What about:
>>
>> static inline struct domain *next_domain_in_cpupool(
>>       struct domain *d, struct cpupool *c)
>> {
>>       for (d = rcu_dereference(d->next_in_list); d&&  d->cpupool != c;
>>            d = rcu_dereference(d->next_in_list));
>>       return d;
>> }
>>
>> #define for_each_domain_in_cpupool(_d,_c)       \
>>    for ( (_d) = rcu_dereference(domain_list);     \
>>          (_d) != NULL;                            \
>>          (_d) = next_domain_in_cpupool((_d), (_c)))
> Same problem as with Keir's variant - you'd enter the loop body for
> the first domain on the list regardless of its cpupool. But with a
> first_domain_in_cpupool() counterpart this might be usable. Or, as
> said in the other reply, putting a more complex construct in the
> middle clause.

I think adding first_domain_in_cpupool() is a good way to go.
Sending out adjusted patch with appropriate locking added in
cpupool_unassign_cpu() soon.


Juergen

-- 
Juergen Gross                 Principal Developer Operating Systems
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