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

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Message-ID: <20121126083634.GA4574@dhcp-192-168-178-175.profitbricks.localdomain>
Date:	Mon, 26 Nov 2012 09:36:34 +0100
From:	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>
To:	Wen Congyang <wencongyang@...il.com>
Cc:	linux-acpi@...r.kernel.org, isimatu.yasuaki@...fujitsu.com,
	wency@...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

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?

> 
> 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?

thanks,

- Vasilis
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