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SubjectRe: [PATCH 4/4] futex: convert hash_bucket locks to raw_spinlock_t
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On Sun, 2010-07-11 at 15:33 +0200, Mike Galbraith wrote:
> On Sat, 2010-07-10 at 21:41 +0200, Mike Galbraith wrote:

> diff --git a/kernel/futex.c b/kernel/futex.c
> index a6cec32..ef489f3 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -2255,7 +2255,14 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
> /* Queue the futex_q, drop the hb lock, wait for wakeup. */
> futex_wait_queue_me(hb, &q, to);
>
> - spin_lock(&hb->lock);
> + /*
> + * Non-blocking synchronization point with futex_requeue().
> + *
> + * We dare not block here because this will alter PI state, possibly
> + * before our waker finishes modifying same in wakeup_next_waiter().
> + */
> + while(!spin_trylock(&hb->lock))
> + cpu_relax();

I agree that this would work. But I wonder if this should have an:

#ifdef PREEMPT_RT
[...]
#else
spin_lock(&hb->lock);
#endif

around it. Or encapsulate this lock in a macro that does the same thing
(just to keep the actual code cleaner)

-- Steve

> ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
> spin_unlock(&hb->lock);
> if (ret)
>
>




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