linux-kernel - Re: [PATCH 0/3] PM, vfs: use filesystem freezing instead of kthread freezer

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Date:	Sat, 31 Oct 2015 12:01:36 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Jiri Kosina <jikos@...nel.org>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>, Tejun Heo <tj@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-pm@...r.kernel.org>
Subject: Re: [PATCH 0/3] PM, vfs: use filesystem freezing instead of kthread
 freezer

On Sat, 31 Oct 2015, Rafael J. Wysocki wrote:

> Runtime PM uses a freezable workqueue, allocated in pm_start_workqueue().
> 
> That's because we don't want async runtime PM to happen during system
> suspend/resume and for good reasons, so if you want to remove the freezing
> mechanism, you need to stop that workqueue at the beginning of dpm_prepare
> and start it again at the end of dpm_complete().

The same sort of thing is true for the USB hub driver's workqueue.  
Since it registers new devices (as a result of hotplugs), it must stop
running at the beginning of the dpm_prepare stage.  Of course, that's
also a workqueue and not a kthread.

Alan Stern

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