linux-kernel - Re: [PATCH 03/39] ocfs2: throttle back local alloc when low on disk space

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Date:	Wed, 1 Oct 2008 23:11:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mark Fasheh <mfasheh@...e.com>
Cc:	linux-kernel@...r.kernel.org, joel.becker@...cle.com,
	ocfs2-devel@....oracle.com, linux-fsdevel@...r.kernel.org,
	mfasheh@...e.com
Subject: Re: [PATCH 03/39] ocfs2: throttle back local alloc when low on disk
 space

> On Wed, 24 Sep 2008 15:00:44 -0700 Mark Fasheh <mfasheh@...e.com> wrote:
> +void ocfs2_local_alloc_seen_free_bits(struct ocfs2_super *osb,
> +				      unsigned int num_clusters)
> +{
> +	spin_lock(&osb->osb_lock);
> +	if (osb->local_alloc_state == OCFS2_LA_DISABLED ||
> +	    osb->local_alloc_state == OCFS2_LA_THROTTLED)
> +		if (num_clusters >= osb->local_alloc_default_bits) {
> +			cancel_delayed_work(&osb->la_enable_wq);
> +			osb->local_alloc_state = OCFS2_LA_ENABLED;
> +		}
> +	spin_unlock(&osb->osb_lock);
> +}
> +
> +void ocfs2_la_enable_worker(struct work_struct *work)
> +{
> +	struct ocfs2_super *osb =
> +		container_of(work, struct ocfs2_super,
> +			     la_enable_wq.work);
> +	spin_lock(&osb->osb_lock);
> +	osb->local_alloc_state = OCFS2_LA_ENABLED;
> +	spin_unlock(&osb->osb_lock);
> +}

cacnel_delayed_work() is a pretty risky function.  The work handler
(ocfs2_la_enable_worker) can execute an arbitrarily long time after
cancel_delayed_work() has returned.  Can all the code here cope with such a
surprise alteration of ->local_alloc_state()?

And you canot use cancel_delayed_work_sync() here due to a deadlock on
->osb_lock().

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