linux-kernel - Re: [lm-sensors] broken suspend [Was: 2.6.24-rc2-mm1]

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Date:	Tue, 20 Nov 2007 08:15:21 -0500
From:	"Mark M. Hoffman" <mhoffman@...htlink.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Rudolf Marek <r.marek@...embler.cz>,
	Jiri Slaby <jirislaby@...il.com>, Greg KH <greg@...ah.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	lm-sensors@...sensors.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [lm-sensors] broken suspend [Was: 2.6.24-rc2-mm1]

Hi all:

* Alan Stern <stern@...land.harvard.edu> [2007-11-19 15:27:14 -0500]:
> On Mon, 19 Nov 2007, Rudolf Marek wrote:
> 
> > Hello all,
> > >>> gives coretemp_cpu_callback -> coretemp_device_remove ->
> > >>> platform_device_unregister, so coretemp seems to be what I have and you don't.
> > > 
> > > Yes.
> > > 
> > > For the coretemp developers: coretemp_cpu_callback() needs to be more 
> > > careful about what it does.  During a system sleep transition (suspend, 
> > > hibernate, resume) it isn't possible to register or unregister a 
> > > device.  Attempts to register will fail and attempts to unregister will 
> > > block until the system sleep is over -- and for this callback that 
> > > means hanging.
> > 
> > Well I wrote the driver. Thanks for the clarification. If I recall correctly I 
> > looked how this part should be done from others drivers. Now while checking
> > what happened to the file, seems Rafael added something related.
> > 
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=8bb7844286fb8c9fce6f65d8288aeb09d03a5e0d
> 
> That does look like it was meant for exactly this sort of situation.
> 
> > > It's not clear what the best way is to fix this.  Perhaps the CPU 
> > > notification should be sent along with a special flag indicating that 
> > > the CPU transition is part of a system sleep (although this seems 
> > > racy).  Perhaps the driver should notice when a system sleep begins, 
> > > and defer all CPU-change handling until after the sleep is over.
> > 
> > maybe it does exist?  CPU_DOWN_PREPARE ?
> > 
> > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/cpu-hotplug.txt;hb=HEAD
> > 
> > Unfortunately I'm not very familiar with this, calling the 
> > coretemp_device_remove from CPU_DOWN_PREPARE would help? Looking at microcode 
> > driver, seems it just hide sysfs interface from user.

AFAICT from that documentation, it would have been better to unregister
the device on CPU_DOWN_PREPARE anyway.  CPU_DEAD seems to be too late -
it's already gone by then.

> I'm not sure exactly what you want to do here.  But it seems like a 
> waste to unregister the coretemp devices at the start of a system sleep 
> and then register them back at the end.
> 
> Could you simply leave the devices registered throughout the entire
> sleep?  Of course, at the end you would have to check that all the CPUs
> really did come back up, and unregister the devices for the CPUs that
> are still offline.

Is it possible to unregister a driver on CPU_DOWN_PREPARE_FROZEN?  If
so, then the simplest fix would be the patch below (Jiri: feel free to
try it). Otherwise it would take a bit of refactoring to bring the sysfs
interface down/up for suspend/resume.

commit ce9c7b78c839a6304696d90083eac08baad524ce
Author: Mark M. Hoffman <mhoffman@...htlink.com>
Date:   Tue Nov 20 07:51:50 2007 -0500

    hwmon: (coretemp) fix suspend/resume hang
    
    Signed-off-by: Mark M. Hoffman <mhoffman@...htlink.com>

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index 5c82ec7..afe2d31 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -338,10 +338,12 @@ static int coretemp_cpu_callback(struct notifier_block *nfb,
 	switch (action) {
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
+	case CPU_DOWN_FAILED:
+	case CPU_DOWN_FAILED_FROZEN:
 		coretemp_device_add(cpu);
 		break;
-	case CPU_DEAD:
-	case CPU_DEAD_FROZEN:
+	case CPU_DOWN_PREPARE:
+	case CPU_DOWN_PREPARE_FROZEN:
 		coretemp_device_remove(cpu);
 		break;
 	}
-- 
Mark M. Hoffman
mhoffman@...htlink.com

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