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SubjectRe: [PATCH RT] locking/rtmutex: don't drop the wait_lock twice
On Thu, 21 Sep 2017 17:48:43 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> Since the futex rework, __rt_mutex_start_proxy_lock() does no longer
> acquire the wait_lock so it must not drop it. Otherwise the lock is not
> only unlocked twice but also the preemption counter is underflown.
>
> Cc: rt-stable@vger.kernel.org
> Reported-by: Gusenleitner Klaus <gus@keba.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> kernel/locking/rtmutex.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index f03876322d4a..79f49d73e4d0 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -2281,7 +2281,6 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
> raw_spin_lock(&task->pi_lock);
> if (task->pi_blocked_on) {
> raw_spin_unlock(&task->pi_lock);
> - raw_spin_unlock_irq(&lock->wait_lock);

Hmm, before this patch, irqs are enabled when returning with -EAGAIN.
But now they are not. Should that be:

raw_spin_unlock_irq(&taks->pi_lock);

or is there something that changes this?

-- Steve


> return -EAGAIN;
> }
> task->pi_blocked_on = PI_REQUEUE_INPROGRESS;

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