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

Mark M. Hoffman
2007-11-20T13:19:29Z

Hi all:

* Alan Stern <stern@rowland.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@lightlink.com>
Date: Tue Nov 20 07:51:50 2007 -0500

hwmon: (coretemp) fix suspend/resume hang

Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.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@lightlink.com