At 11/26/2012 04:36 PM, Vasilis Liaskovitis Wrote:

On Sun, Nov 25, 2012 at 12:20:47AM +0800, Wen Congyang wrote:

quoted

At 2012/11/24 1:50, Vasilis Liaskovitis Wrote:

quoted

Consider the following sequence of operations for a hotplugged memory device:

1. echo "PNP0C80:XX">  /sys/bus/acpi/drivers/acpi_memhotplug/unbind
2. echo "PNP0C80:XX">  /sys/bus/acpi/drivers/acpi_memhotplug/bind
3. echo 1>/sys/bus/pci/devices/PNP0C80:XX/eject

The driver is successfully re-bound to the device in step 2. However step 3 will
not attempt to remove the memory. This is because the acpi_memory_info enabled
bit for the newly bound driver has not been set to 1. This bit needs to be set
in the case where the memory is already used by the kernel (add_memory returns
-EEXIST)

Hmm, I think the reason is that we don't offline/remove memory when
unbinding it
from the driver. I have sent a patch to fix this problem, and this patch
is in
pm tree now. With this patch, we will offline/remove memory when
unbinding it from
the drriver.

ok. Which patch is this? Does it require driver-core changes?

https://lkml.org/lkml/2012/11/15/21

Patch 1-6 is in pm tree now.

quoted

Consider the following sequence of operations for a hotplugged memory
device:

1. echo "PNP0C80:XX" > /sys/bus/acpi/drivers/acpi_memhotplug/unbind
2. echo 1 >/sys/bus/pci/devices/PNP0C80:XX/eject

If we don't offline/remove the memory, we have no chance to do it in
step 2. After
step2, the memory is used by the kernel, but we have powered off it. It
is very
dangerous.

How does power-off happen after unbind? acpi_eject_store checks for existing
driver before taking any action:

#ifndef FORCE_EJECT
	if (acpi_device->driver == NULL) {
		ret = -ENODEV;
		goto err;
	}
#endif

FORCE_EJECT is not defined afaict, so the function returns without scheduling
acpi_bus_hot_remove_device. Is there another code path that calls power-off?

Consider the following case:

We hotremove the memory device by SCI and unbind it from the driver at the same time:

CPUa                                                  CPUb
acpi_memory_device_notify()
                                       unbind it from the driver
    acpi_bus_hot_remove_device()

Thanks
Wen Congyang

thanks,

- Vasilis

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