linux-kernel - Re: [PATCH 4/6 v2] PM: Limit race conditions between runtime PM and system sleep (v2)

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Message-Id: <201111030128.52823.rjw@sisk.pl>
Date:	Thu, 3 Nov 2011 01:28:52 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Greg KH <greg@...ah.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Kevin Hilman <khilman@...com>, linux-scsi@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>, stable@...nel.org,
	Ulf Hansson <Ulf.Hansson@...ricsson.com>
Subject: Re: [PATCH 4/6 v2] PM: Limit race conditions between runtime PM and system sleep (v2)

On Wednesday, November 02, 2011, Greg KH wrote:
> On Wed, Nov 02, 2011 at 10:00:39PM +0100, Linus Walleij wrote:
> > On Wed, Nov 2, 2011 at 9:11 PM, Greg KH <greg@...ah.com> wrote:
> > > On Wed, Nov 02, 2011 at 09:06:02PM +0100, Linus Walleij wrote:
> > >> On Wed, Nov 2, 2011 at 8:14 PM, Greg KH <greg@...ah.com> wrote:
> > >> > So, what specific git commits do you want to see in the 3.0-stable
> > >> > tree, and in what order should they be applied in?
> > >>
> > >> So to my untrained eye it looks like it should be applied like this (top to
> > >> bottom) using the reverse commit order from the mainline kernel:
> > >>
> > >> e529192 PM: Introduce generic "noirq" callback routines for subsystems (v2)
> > >> 455716e PM / Runtime: Update documentation of interactions with system sleep
> > >> 1e2ef05 PM: Limit race conditions between runtime PM and system sleep (v2)
> > >> f3393b6 PM / Runtime: Add new helper function: pm_runtime_status_suspended()
> > >>
> > >> So (2) documents the problem, (3) fixes it, whereas (1) and (4) makes
> > >> it possible
> > >> to write proper _noirq() code that does not race, IIRC.
> > >
> > > But, after this, it's just adding new infrastructure that drivers will
> > > then be able to use.  As I'm not adding new drivers to 3.0, there will
> > > not be any users of this code, so why add it in the first place?  It
> > > doesn't look like this follows the rules of the stable kernel tree at
> > > all, does it?
> > 
> > We'll have to get some feedback from Rafael, but the way I percieved
> > it, the patch (2) fixes a very real race, then fixing that makes it
> > necessary for drivers using runtime_pm to do things differently to
> > be on the safe side. But none were really fixed when first merging
> > it.
> > 
> > So on second thought you probably only want patch (2)
> > "PM: Limit race conditions between runtime PM and system sleep (v2)"
> > for stable.
> 
> Ok, Rafael, any objection to me applying just this one?

Well, I'd prefer not to unless there are reports confirming user problems
being fixed specifically by this patch.  It changes the PM core's behavior
quite significantly and I'm a little afraid of possible regressions that may
result from it.

Thanks,
Rafael
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