linux-kernel - Re: [PATCH] ACPI / scan: Make it clear that acpi_bus

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Date:	Mon, 18 Feb 2013 15:53:41 +0100
From:	Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Toshi Kani <toshi.kani@...com>, Jiang Liu <liuj97@...il.com>,
	wency@...fujitsu.com
Subject: Re: [PATCH] ACPI / scan: Make it clear that acpi_bus_trim() cannot
 fail

On Mon, Feb 18, 2013 at 02:17:02PM +0100, Rafael J. Wysocki wrote:
> On Monday, February 18, 2013 01:25:49 PM Vasilis Liaskovitis wrote:
> > Hi,
> > 
> > On Thu, Jan 24, 2013 at 11:56:50PM +0100, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > 
> > > Since acpi_bus_trim() cannot fail, change its definition to a void
> > > function, so that its callers don't check the return value in vain
> > > and update the callers.
> > 
> > I have missed a few patchsets/discussions in the last month and wanted to
> > ask a question related to this: Does the new always-succeed 2-pass
> > trim_device design guarantee safe memory hot-remove operations?
> 
> I doesn't by itself.  Nor it really can, because the .remove() callbacks of
> device drivers are not allowed to fail.

right.

> 
> > Afaict if memory offline fails now, the device is ejected (_EJ0) anyways
> > causing a panic. Tested in a VM with linux-next-20130207 and
> > linux-next-20130218 by doing an SCI-eject request on a hot-plugged dimm.
> > 
> > Are there more patches in development for safe memory hot-remove?
> 
> Yes, there are.  I sent a patch series yesterday introducing some safety
> measures (you can disable memory hotplug from user space or disable
> automatic ejection).  There's more to come still.
> 
> The plan is to introduce offline/online operations for memory modules (in
> analogy with CPU core online/offline) that can be started by user space and
> memory eject will only be possible after offline (i.e. when the memory module
> is known to be not in use).

ok, thanks for the info. I 'll test these and the follow ups.

thanks again,

- Vasilis
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