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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Linux-pm mailing list <linux-pm@lists.linux-foundation.org>,
Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: [linux-pm] Fundamental flaw in system suspend, exposed by freezer removal
Date: Mon, 25 Feb 2008 23:25:09 +0100 [thread overview]
Message-ID: <200802252325.09439.rjw@sisk.pl> (raw)
In-Reply-To: <Pine.LNX.4.44L0.0802251439030.5536-100000@iolanthe.rowland.org>
On Monday, 25 of February 2008, Alan Stern wrote:
> On Mon, 25 Feb 2008, Alan Stern wrote:
>
> > The only possible solution is to have the drivers themselves be
> > responsible for preventing calls to device_add() or device_register()
> > during a system sleep. (It's also necessary to prevent driver binding,
> > but this isn't a major issue.) The most straightforward approach is to
> > add a new pair of driver methods: one to disable adding children and
> > one to re-enable it. Of course this would represent a significant
> > addition to the Power Management driver interface.
> >
> > (Note that the existing suspend and resume methods cannot be used for
> > this purpose. Drivers assume that when the suspend method is called,
> > it has already been called for all the child devices. This wouldn't be
> > true if one of the purposes of the method was to prevent addition of
> > new children.)
>
> On further thought maybe the existing methods can be used, with care.
> Drivers would have to assume the responsibility of synchronizing with
> their helper threads and stopping addition of new children (something
> they should already be doing), and they would also have to check that
> all the existing children are already suspended. They should not make
> the assumption that the PM core has already suspended all the children.
IMO the device driver should assure that no new children will be registered
concurrently with the ->suspend() method (IOW, ->suspend() should wait for
all such registrations to complete and should prevent any new ones from
being started) and it should make it impossible to register any new children
after ->suspend() has run. It's the driver's problem how to achieve that.
> The PM core could help detect errors here. If it tries to suspend a
> device and sees that the device's parent is already suspended, then the
> parent's driver has a bug.
Yes, I think we ought to fail the suspend in such cases. Still, that's not
sufficient to prevent a child from being registered after we've run
dpm_suspend(). For this reason, we could also leave dpm_suspend() with
dpm_list_mtx held and not release it until the next dpm_resume() is run.
That will potentially cause some trouble to CPU hotplug cotifiers, but we can
handle that, for example, by using the in_suspend_context() test.
Thanks,
Rafael
next prev parent reply other threads:[~2008-02-25 22:26 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-25 15:39 Alan Stern
2008-02-25 19:46 ` [linux-pm] " Alan Stern
2008-02-25 22:25 ` Rafael J. Wysocki [this message]
2008-02-25 23:37 ` Alan Stern
2008-02-26 0:07 ` Rafael J. Wysocki
2008-02-26 15:49 ` Alan Stern
2008-02-26 23:17 ` Rafael J. Wysocki
2008-02-27 16:03 ` Alan Stern
2008-02-27 19:50 ` Rafael J. Wysocki
2008-02-27 20:15 ` Alan Stern
2008-02-28 22:49 ` Alan Stern
2008-02-29 0:01 ` Rafael J. Wysocki
2008-02-29 14:26 ` Rafael J. Wysocki
2008-02-29 15:53 ` Alan Stern
2008-02-29 17:02 ` Rafael J. Wysocki
2008-02-29 18:42 ` Alan Stern
2008-02-29 21:57 ` Rafael J. Wysocki
2008-02-29 22:46 ` Alan Stern
2008-03-01 0:13 ` Rafael J. Wysocki
2008-03-01 15:30 ` Alan Stern
2008-03-02 13:37 ` Rafael J. Wysocki
2008-03-02 16:22 ` Alan Stern
2008-03-02 19:11 ` Rafael J. Wysocki
2008-03-03 3:54 ` Alan Stern
2008-03-03 16:32 ` Rafael J. Wysocki
2008-03-03 17:43 ` Alan Stern
2008-03-03 20:47 ` Rafael J. Wysocki
2008-03-03 22:48 ` Alan Stern
2008-03-03 22:56 ` Rafael J. Wysocki
2008-03-03 23:12 ` Alan Stern
2008-03-03 23:18 ` Rafael J. Wysocki
2008-02-26 7:13 ` David Brownell
2008-02-26 8:25 ` David Newall
2008-02-26 9:16 ` David Brownell
2008-02-26 13:36 ` David Newall
2008-02-26 15:58 ` Alan Stern
2008-02-25 22:24 ` Rafael J. Wysocki
2008-02-27 20:36 ` Benjamin Herrenschmidt
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