thread-safety of rtems_cpu_usage_report

[Joel Sherrill]

Till Straumann wrote:
> Joel Sherrill wrote:
>   
>> Till Straumann wrote:
>>     
>>> Joel Sherrill wrote:
>>>  
>>>       
>>>> Till Straumann wrote:
>>>>    
>>>>         
>>>>> I look at rtems_cpu_usage_report() and it
>>>>> seems to me that the code merrily scans
>>>>> the _Objects_Information_table and accesses
>>>>> the Thread_Control blocks it finds there
>>>>> w/o using any kind of protection.
>>>>>
>>>>> What happens, e.g., if the _Objects_Information_table
>>>>> gets extended or otherwise modified by another
>>>>> thread while the code is scanning the table?
>>>>>
>>>>> Am I missing something?
>>>>>         
>>>>>           
>>>> no. :(
>>>>
>>>> I had always wanted to change it to a loop
>>>> from min to max id around a "get cpu use"
>>>> task id based information call. Then it
>>>> can fail on each one.
>>>>
>>>> But anything using iterate over all tasks is
>>>> not thread safe. Perhaps it would be best
>>>> to put that call in an allocation critical section.
>>>> Then the set cannot change since there are
>>>> no create/delete's allowed.
>>>>     
>>>>         
>>> Definitely deserves some thought.
>>> E.g., 'sync' looks quite a bit scary...
>>>   
>>>       
>> I think using the allocation mutex would
>> prevent any issues here also.  You wouldn't be
>> able to malloc memory or create threads.
>>     
> Which is why it's scary. Doing any I/O should
> not delay malloc or thread creation.
>
>   
The first alternative I mentioned which was
to have a "get object class info" and loop
from min to max id calling "task get cpu use"
would avoid all of this but it is more work
to implement.

Each fetch of the information would itself
be in a critical section.  But the entire
operation wouldn't need to be.
> T.
>   
>>> T.
>>>
>>>  
>>>       
>>>>> -- Till
>>>>> _______________________________________________
>>>>> rtems-users mailing list
>>>>> rtems-users at rtems.com
>>>>> http://rtems.rtems.org/mail
>>>>>         
>>>>>           
>>>>     
>>>>         
>>>   
>>>       
>>     
>
>   


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Joel Sherrill, Ph.D.             Director of Research & Development
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