linux-kernel - Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Message-ID: <Pine.LNX.4.44L0.0707061034540.3737-100000@iolanthe.rowland.org>
Date:	Fri, 6 Jul 2007 10:38:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH] Remove process freezer from suspend to RAM pathway

On Fri, 6 Jul 2007, Benjamin Herrenschmidt wrote:

> What you propose is basically a slightly over-simplistic version of what
> I think (and Paulus think) should be done. We do need to do it via
> driver callbacks down the tree since only drivers can know how to deal
> with their DMA etc... and ordering need to be respected, but that's
> basically it.
> 
> And guess what ? It's what we do on powerbooks, and it works fine,
> without a freezer :-)

I wish you'd stop saying that.  Have you ever done any serious testing?

Here's something to try:  Add a time delay to the end of hub_suspend in
drivers/usb/core/hub.c, so you can provoke a race manually.  Then while
one of your root hubs is being suspended and the system is waiting in
that delay, either plug in a new USB device to that hub or unplug an
existing device.

Be sure that CONFIG_USB_DEBUG is on so that we can figure out what 
happened after the fact.

Alan Stern

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