linux-kernel - Re: [RFC PATCH v3 3/3] acpi_memhotplug: Allow eject to proceed on rebind scenario

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Date:	Mon, 26 Nov 2012 17:11:26 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>
CC:	Wen Congyang <wencongyang@...il.com>, linux-acpi@...r.kernel.org,
	isimatu.yasuaki@...fujitsu.com, rjw@...k.pl, lenb@...nel.org,
	toshi.kani@...com, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v3 3/3] acpi_memhotplug: Allow eject to proceed on
 rebind scenario

At 11/26/2012 04:36 PM, Vasilis Liaskovitis Wrote:
> On Sun, Nov 25, 2012 at 12:20:47AM +0800, Wen Congyang wrote:
>> At 2012/11/24 1:50, Vasilis Liaskovitis Wrote:
>>> 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.

> 
>>
>> 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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