Date: Mon, 7 Jan 2013 09:47:20 -0800
From: Tejun Heo <tj@kernel.org>
To: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: linux-nfs@vger.kernel.org, Weston Andros Adamson <dros@netapp.com>,
        Bruce Fields <bfields@fieldses.org>
Subject: Re: [PATCH 1/3] SUNRPC: Ensure that we free the rpc_task after
 cleanups are done
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On Fri, Jan 04, 2013 at 01:15:00PM -0500, Trond Myklebust wrote:
> This patch ensures that we free the rpc_task after the cleanup callbacks
> are done in order to avoid a deadlock problem that can be triggered if
> the callback needs to wait for another workqueue item to complete.
> 
> Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
> Cc: Weston Andros Adamson <dros@netapp.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Bruce Fields <bfields@fieldses.org>
> Cc: stable@vger.kernel.org

Acked-by: Tejun Heo <tj@kernel.org>

> + * Tejun Heo states:
> + * "Workqueue currently considers two work items to be the same if they're
> + * on the same address and won't execute them concurrently - ie. it
> + * makes a work item which is queued again while being executed wait
> + * for the previous execution to complete.
> + *
> + * If a work function frees the work item, and then waits for an event
> + * which should be performed by another work item and *that* work item
> + * recycles the freed work item, it can create a false dependency loop.
> + * There really is no reliable way to detect this short of verifying
> + * every memory free."

I will document it in Documentation/workqueue.txt.

Thanks!

-- 
tejun