linux-kernel - Re: [PATCH v4] pm_qos: make update

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Message-ID: <20100609180033.39d5b499@schatten.dmk.lab>
Date:	Wed, 9 Jun 2010 18:00:33 +0200
From:	Florian Mickler <florian@...kler.org>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	markgross@...gnar.org, mgross@...ux.intel.com,
	linville@...driver.com, Frederic Weisbecker <fweisbec@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] pm_qos: make update_request non blocking

On Wed, 09 Jun 2010 11:37:12 -0400
James Bottomley <James.Bottomley@...e.de> wrote:

> This still isn't resilient against two successive calls to update.  If
> the second one gets to schedule_work() before the work of the first one
> has finished, you'll corrupt the workqueue.

Sorry, I don't see it. Can you elaborate?

In "run_workqueue(" we do a list_del_init() which resets the
list-pointers of the workitem and only after that reset the
WORK_STRUCT_PENDING member of said structure. 

schedule_work does a queue_work_on which does a test_and_set_bit on
the WORK_STRUCT_PENDING member of the work and only queues the work
via list_add_tail in insert_work afterwards.

Where is my think'o? Or was this fixed while you didn't look?

So what _can_ happen, is that we miss a new notfication while the old
notification is still in the queue. But I don't think this is a problem.

Cheers,
Flo
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