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    SubjectRe: [lm-sensors] broken suspend [Was: 2.6.24-rc2-mm1]
    Date
    On Tuesday, 20 of November 2007, Mark M. Hoffman wrote:
    > 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?

    No. In that case the suspend core is holding the device's mutex and your
    attempt to unregister it will deadlock with it.

    Do you _have_ _to_ unregister the device at all? Why don't you just leave
    it registered on CPU_DOWN_PREPARE_FROZEN? The CPU is not going away
    physically in this case and it's _guaranteed_ that _cpu_up() will be called on
    it as soon as the hibernation image is ready or we are back from suspend.

    > 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>

    I'd do it like this:

    > 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:
    > coretemp_device_add(cpu);
    + case CPU_DOWN_FAILED_FROZEN:
    > break;
    > - case CPU_DEAD:
    > - case CPU_DEAD_FROZEN:
    > + case CPU_DOWN_PREPARE:
    > coretemp_device_remove(cpu);
    + case CPU_DOWN_PREPARE_FROZEN:
    > break;
    > }

    Greetings,
    Rafael


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