Re: PROBLEM: Bug in __pollwait() can cause select() and poll()

[Andrew Morton]

Ray Bryant <[e-mail]> wrote:
>
>  > The correct fix is current->state = TASK_RUNNING just before calling
>  > yield() in the rebalance code.
> 
>  But doesn't this have the same kind of problem?  e. g., just before
>  calling yield() in the rebalance code we save current->state, set it to
>  TASK_RUNNING, then restore current->state on return from yield().  If a
>  fd becomes ready after the call to yield(), and we entered
>  __alloc_pages() with state TASK_INTERRUPTIBLE, aren't we in exactly the
>  same situation as described above?

No, you cannot restore the task state after having set it to TASK_RUNNING.

Just leave the state at TASK_RUNNING.  The (silly) code which called the
page allocator in state TASK_[IN]TERRUPTIBLE will just go around its wait
loop an extra time and go back to sleep.  This almost always works.