linux-kernel - Re: [PATCH -v5 12/14] futex,rt_mutex: Restructure rt_mutex_finish_proxy

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Message-ID: <alpine.DEB.2.20.1703071516080.3584@nanos>
Date:   Tue, 7 Mar 2017 15:18:46 +0100 (CET)
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, dvhart@...radead.org
Subject: Re: [PATCH -v5 12/14] futex,rt_mutex: Restructure
 rt_mutex_finish_proxy_lock()

On Sat, 4 Mar 2017, Peter Zijlstra wrote:
> +/**
> + * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
> + * @lock:		the rt_mutex we were woken on
> + * @waiter:		the pre-initialized rt_mutex_waiter
> + *
> + * Clean up the failed lock acquisition as per rt_mutex_wait_proxy_lock().
> + *
> + * Returns:
> + *  true  - did the cleanup, we done.
> + *  false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
> + *          caller should disregards its return value.

Hmm. How would that happen? Magic owner assignement to a non waiter? The
callsite only calls here in the failed case.

I must be missing something

Thanks,

	tglx

> + *
> + * Special API call for PI-futex support
> + */
> +bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
> +				 struct rt_mutex_waiter *waiter)
> +{
> +	bool cleanup = false;
> +
> +	raw_spin_lock_irq(&lock->wait_lock);
> +	/*
> +	 * If we acquired the lock, no cleanup required.
> +	 */
> +	if (rt_mutex_owner(lock) != current) {
> +		remove_waiter(lock, waiter);
> +		fixup_rt_mutex_waiters(lock);
> +		cleanup = true;
> +	}
> +	raw_spin_unlock_irq(&lock->wait_lock);
> +
> +	return cleanup;
> +}