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SubjectRe: [patch] scheduler fixes, 2.5.32-BK

> - changes the migration code to use struct completion. Andrew pointed out
> that there might be a small window in where the up() touches the
> semaphore while the waiting task goes on and frees its stack. And
> completion is more suited for this kind of stuff anyway.

actually, i think the race does not exist. up() is perfectly safely done
on the on-stack semaphore, because both the wake_up() done by __up() and
the __down() path takes the waitqueue spinlock, so i cannot see where the
up() touches the semaphore after the down()-ed task has been woken up.

the second argument still holds though - a completion is probably slightly
cheaper in this case.

Ingo

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