linux-kernel - Re: [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK

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Date:   Sat, 8 Oct 2016 20:22:38 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     mingo@...nel.org, juri.lelli@....com, rostedt@...dmis.org,
        xlpang@...hat.com, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
        jdesfossez@...icios.com, bristot@...hat.com
Subject: Re: [RFC][PATCH 4/4] futex: Rewrite FUTEX_UNLOCK_PI

On Fri, 7 Oct 2016, Peter Zijlstra wrote:
> +		/*
> +		 * Grab a reference on the pi_state and drop hb->lock.
> +		 *
> +		 * The reference ensures pi_state lives, dropping the hb->lock
> +		 * is tricky.. wake_futex_pi() will take rt_mutex::wait_lock to
> +		 * close the races against futex_lock_pi(), but in case of
> +		 * _any_ fail we'll abort and retry the whole deal.
> +		 */
> +		WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
> +		spin_unlock(&hb->lock);
> +
> +		ret = wake_futex_pi(uaddr, uval, pi_state);
> +
> +		put_pi_state(pi_state);
> +
>  		/*
>  		 * In case of success wake_futex_pi dropped the hash
>  		 * bucket lock.

This comment has become stale.

Thanks,

	tglx