Re: [PATCH][RFC]: mutex: adaptive spin

[Steven Rostedt]

> 
> Btw, this also fixes a bug: your patch did
> 
> 	+                     __set_task_state(task, state);
> 	+                     /* didnt get the lock, go to sleep: */
> 	+                     schedule();
> 
> for the schedule case without holding the mutex spinlock.
> 
> And that seems very buggy and racy indeed: since it doesn't hold the mutex 
> lock, if the old owner releases the mutex at just the right point (yeah, 
> yeah, it requires a scheduling event on another CPU in order to also miss 
> the whole "task_is_current()" logic), the wakeup can get lost, because you 
> set the state to sleeping perhaps _after_ the task just got woken up. So 
> we stay sleeping even though the mutex is clear.


That is indeed a bug.

Peter, why did you need to move __set_task_state down here?  The -rt patch 
does not do this.

-- Steve
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