Re: mpol_to_str revisited.

On Mon, 15 Oct 2012, KOSAKI Motohiro wrote:

I don't think 80de7c3138ee9fd86a98696fd2cf7ad89b995d0a is right fix.

It's certainly not a complete fix, but I think it's a much better result 
of the race, i.e. we don't panic anymore, we simply fail the read() 
instead.

we should
close a race (or kill remain ref count leak) if we still have.

As I mentioned earlier in the thread, the read() is done here on a task 
while only a reference to the task_struct is taken and we do not hold 
task_lock() which is required for task->mempolicy.  Once that is fixed, 
mpol_to_str() should never be called for !task->mempolicy so it will never 
need to return -EINVAL in such a condition.

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