Re: Lots of bugs with current->state = TASK_*INTERRUPTIBLE

David Daney
2010-01-21T20:21:45Z

>>
>> This is what I thought.
>>
>> My cpu (Cavium Octeon) does not have out of order reads, so my wmb() is
>
> Can you have reads that are out of order wrt writes? Because the above
> does not have out of order reads. It just had a read that came before a
> write. The above code could look like:
>
> (hypothetical assembly language)
>
> ld r2, TASK_UNINTERRUPTIBLE
> st r2, (current->state)
> wmb
> ld r1, (x)
> cmp r1, 0
>
> Is it possible for the CPU to do the load of r1 before storing r2? If
> so, then the bug still exists.
>

Indeed it is. Lockless operations make my head hurt.

Thanks for clarifying.

David Daney

> -- Steve
>
>
>> in fact a full mb() from the point of view of the current CPU. So I
>> think I could weaken my bariers in set_current_state() and still get
>> correct operation. However as you say...
>>
>
>
>