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Subject: Re: [PATCH 12/15] block: introduce blk-iolatency io controller
To:     Josef Bacik <josef@toxicpanda.com>, linux-block@vger.kernel.org,
        kernel-team@fb.com, akpm@linux-foundation.org, hannes@cmpxchg.org,
        linux-kernel@vger.kernel.org, tj@kernel.org,
        linux-fsdevel@vger.kernel.org
Cc:     Josef Bacik <jbacik@fb.com>
References: <20180625151243.2132-1-josef@toxicpanda.com>
 <20180625151243.2132-13-josef@toxicpanda.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <05a581ed-8f21-9d89-a813-a03d802d3469@kernel.dk>
Date:   Wed, 27 Jun 2018 13:06:31 -0600
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On 6/25/18 9:12 AM, Josef Bacik wrote:
> +static void __blkcg_iolatency_throttle(struct rq_qos *rqos,
> +				       struct iolatency_grp *iolat,
> +				       spinlock_t *lock, bool issue_as_root,
> +				       bool use_memdelay)
> +	__releases(lock)
> +	__acquires(lock)
> +{
> +	struct rq_wait *rqw = &iolat->rq_wait;
> +	unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay);
> +	DEFINE_WAIT(wait);
> +	bool first_block = true;
> +
> +	if (use_delay)
> +		blkcg_schedule_throttle(rqos->q, use_memdelay);
> +
> +	/*
> +	 * To avoid priority inversions we want to just take a slot if we are
> +	 * issuing as root.  If we're being killed off there's no point in
> +	 * delaying things, we may have been killed by OOM so throttling may
> +	 * make recovery take even longer, so just let the IO's through so the
> +	 * task can go away.
> +	 */
> +	if (issue_as_root || fatal_signal_pending(current)) {
> +		atomic_inc(&rqw->inflight);
> +		return;
> +	}
> +
> +	if (iolatency_may_queue(iolat, &wait, first_block))
> +		return;
> +
> +	do {
> +		prepare_to_wait_exclusive(&rqw->wait, &wait,
> +					  TASK_UNINTERRUPTIBLE);
> +
> +		iolatency_may_queue(iolat, &wait, first_block);
> +		first_block = false;
> +
> +		if (lock) {
> +			spin_unlock_irq(lock);
> +			io_schedule();
> +			spin_lock_irq(lock);
> +		} else {
> +			io_schedule();
> +		}
> +	} while (1);

So how does this wait loop ever exit?

-- 
Jens Axboe