Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand unprotected when accessed by /proc)

Oleg Nesterov
2014-06-11T17:18:59Z

On 06/11, Oleg Nesterov wrote:
>
> On 06/11, Paul E. McKenney wrote:
>
> > raw_spin_unlock_irqrestore(&rnp->lock, flags);
> > rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
> > rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
> >
> > + /* Wait until boostee is done accessing mtx before reinitializing. */
> > + wait_for_completion(&rnp->boost_completion);
> > +
>
> I must have missed something, I dont understand why we need ->boost_completion.
>
> What if you simply move that rt_mutex into rcu_node ?
>
> Or. Given that rcu_boost_kthread() never exits, it can declare this mutex
> on stack and pass the pointer to rcu_boost() ?

Ah, please ignore, I forgot about init_proxy_locked(). Although perhaps this
can be solved easily.

Oleg.