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

On 11/17/2011 03:32 PM, Jan Beulich wrote:

On 17.11.11 at 15:04, Juergen Gross<juergen.gross@xxxxxxxxxxxxxx>  wrote:

On 11/17/2011 02:52 PM, Keir Fraser wrote:

On 17/11/2011 13:30, "Jan Beulich"<JBeulich@xxxxxxxx>   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
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html


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