linux-kernel - Re: [PATCH 10/13] block, cfq: unlink cfq_io

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Date:	Wed, 26 Oct 2011 15:48:57 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, ctalbott@...gle.com, rni@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/13] block, cfq: unlink cfq_io_context's immediately

On Tue, Oct 25, 2011 at 06:48:36PM -0700, Tejun Heo wrote:

[..]
> +/*
> + * Slow path for ioc release in put_io_context().  Performs double-lock
> + * dancing to unlink all cic's and then frees ioc.
> + */
> +static void ioc_release_fn(struct work_struct *work)
>  {
> -	if (!hlist_empty(&ioc->cic_list)) {
> -		struct cfq_io_context *cic;
> +	struct io_context *ioc = container_of(work, struct io_context,
> +					      release_work);
> +	struct request_queue *last_q = NULL;
> +
> +	spin_lock_irq(&ioc->lock);
> +
> +	while (!hlist_empty(&ioc->cic_list)) {
> +		struct cfq_io_context *cic = hlist_entry(ioc->cic_list.first,
> +							 struct cfq_io_context,
> +							 cic_list);
> +		if (cic->q != last_q) {
> +			struct request_queue *this_q = cic->q;
> +
> +			/*
> +			 * Need to switch to @this_q.  Once we release
> +			 * @ioc->lock, it can go away along with @cic.
> +			 * Hold on to it.
> +			 */
> +			__blk_get_queue(this_q);
> +
> +			/*
> +			 * blk_put_queue() might sleep thanks to kobject
> +			 * idiocy.  Always release both locks, put and
> +			 * restart.
> +			 */
> +			if (last_q) {
> +				spin_unlock(last_q->queue_lock);
> +				spin_unlock_irq(&ioc->lock);
> +				blk_put_queue(last_q);
> +			} else {
> +				spin_unlock_irq(&ioc->lock);
> +			}
> +
> +			last_q = this_q;
> +			spin_lock_irq(this_q->queue_lock);
> +			spin_lock(&ioc->lock);
> +			continue;
> +		}
> +		ioc_release_depth_inc(cic->q);
> +		cic->exit(cic);
> +		cic->release(cic);
> +		ioc_release_depth_dec(cic->q);

cic->release(cic) can free the cic? Are we accessing cic after freeing it
up in ioc_release_depth_dec(cic->q);

Thanks
Vivek
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