linux-kernel - Re: Cannot hot remove a memory device

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Date:	Fri, 02 Aug 2013 15:46:15 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	rafael.j.wysocki@...el.com, vasilis.liaskovitis@...fitbricks.com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	tangchen@...fujitsu.com, wency@...fujitsu.com
Subject: Re: Cannot hot remove a memory device

On Thu, 2013-08-01 at 23:43 +0200, Rafael J. Wysocki wrote:
> Hi,
> 
> Thanks for your report.
> 
> On Thursday, August 01, 2013 05:37:21 PM Yasuaki Ishimatsu wrote:
> > By following commit, I cannot hot remove a memory device.
> > 
> > ACPI / memhotplug: Bind removable memory blocks to ACPI device nodes
> > commit e2ff39400d81233374e780b133496a2296643d7d
> > 
> > Details are follows:
> > When I add a memory device, acpi_memory_enable_device() always fails
> > as follows:
> > 
> > ...
> > [ 1271.114116]  [ffffea121c400000-ffffea121c7fffff] PMD -> [ffff880813c00000-ffff880813ffffff] on node 3
> > [ 1271.128682]  [ffffea121c800000-ffffea121cbfffff] PMD -> [ffff880813800000-ffff880813bfffff] on node 3
> > [ 1271.143298]  [ffffea121cc00000-ffffea121cffffff] PMD -> [ffff880813000000-ffff8808133fffff] on node 3
> > [ 1271.157799]  [ffffea121d000000-ffffea121d3fffff] PMD -> [ffff880812c00000-ffff880812ffffff] on node 3
> > [ 1271.172341]  [ffffea121d400000-ffffea121d7fffff] PMD -> [ffff880812800000-ffff880812bfffff] on node 3
> > [ 1271.186872]  [ffffea121d800000-ffffea121dbfffff] PMD -> [ffff880812400000-ffff8808127fffff] on node 3
> > [ 1271.201481]  [ffffea121dc00000-ffffea121dffffff] PMD -> [ffff880812000000-ffff8808123fffff] on node 3
> > [ 1271.216041]  [ffffea121e000000-ffffea121e3fffff] PMD -> [ffff880811c00000-ffff880811ffffff] on node 3
> > [ 1271.230623]  [ffffea121e400000-ffffea121e7fffff] PMD -> [ffff880811800000-ffff880811bfffff] on node 3
> > [ 1271.245148]  [ffffea121e800000-ffffea121ebfffff] PMD -> [ffff880811400000-ffff8808117fffff] on node 3
> > [ 1271.259683]  [ffffea121ec00000-ffffea121effffff] PMD -> [ffff880811000000-ffff8808113fffff] on node 3
> > [ 1271.274194]  [ffffea121f000000-ffffea121f3fffff] PMD -> [ffff880810c00000-ffff880810ffffff] on node 3
> > [ 1271.288764]  [ffffea121f400000-ffffea121f7fffff] PMD -> [ffff880810800000-ffff880810bfffff] on node 3

It appears that each memory object only has 64MB of memory.  This is
less than the memory block size, which is 128MB.  This means that a
single memory block associates with two ACPI memory device objects.

> > ...	
> > [ 1271.325841] acpi PNP0C80:03: acpi_memory_enable_device() error
> 
> Well, the only new way acpi_memory_enable_device() can fail after that commit
> is a failure in acpi_bind_memory_blocks().

Agreed.

> This means that either handle is NULL, which I think we can exclude, because
> acpi_memory_enable_device() wouldn't be called at all if that were the case, or
> there's a more subtle error in acpi_bind_one().
> 
> One that comes to mind is that we may be calling acpi_bind_one() twice for the
> same memory region, in which it will trigger -EINVAL from the sanity check in
> there.

I think it fails with -EINVAL at the place with dev_warn(dev, "ACPI
handle is already set\n").  When two ACPI memory objects associate with
a same memory block, the bind procedure of the 2nd ACPI memory object
sees that ACPI_HANDLE(dev) is already set to the 1st ACPI memory object.

Thanks,
-Toshi

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