linux-kernel - Re: kdump failed because of hotplug memory adding in kdump kernel

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Date:	Thu, 9 Jan 2014 09:48:20 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Baoquan <bhe@...hat.com>, linux-acpi@...r.kernel.org,
	zhangyanfei@...fujitsu.com, tangchen@...fujitsu.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dyoung@...hat.com
Subject: Re: kdump failed because of hotplug memory adding in kdump kernel

On Thu, Jan 09, 2014 at 12:07:17AM +0100, Rafael J. Wysocki wrote:
> On Wednesday, January 08, 2014 10:58:29 AM Vivek Goyal wrote:
> > On Wed, Jan 08, 2014 at 11:26:43PM +0800, Baoquan wrote:
> > 
> > [..]
> > > [    1.592222] acpi PNP0A03:03: fail to add MMCONFIG information, can't access extended PCI configuration space under this bridge.
> > > [    1.605045] PCI host bridge to bus 0000:ff
> > > [    1.609615] pci_bus 0000:ff: root bus resource [bus ff]
> > > [    1.632117] System RAM resource [mem 0x01000000-0x7bffffff] cannot be added
> > > [    1.639892] init_memory_mapping: [mem 0x100000000-0x87fffffff]
> > > [    1.717793] swapper/0: page allocation failure: order:9, mode:0x84d0
> > > [    1.724884] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.10.0-59.el7.x86_64 #1
> > > [    1.732842] Hardware name: QCI QSSC-S4R/QSSC-S4R, BIOS QSSC-S4R.QCI.01.00.S001.032520101647 03/25/2010
> > > [    1.743224]  0000000000000000 ffff8800339878c8 ffffffff815b64ad ffff880033987950
> > > [    1.751513]  ffffffff8113a980 ffff88003673ab28 00000000000001fe 0000000000000001
> > > [    1.759804]  ffff880000000040 ffffffff810bc28a 0000000000000000 0000000000000200
> > > [    1.768096] Call Trace:                                                                                                                                            [348/1928]
> > > [    1.770834]  [<ffffffff815b64ad>] dump_stack+0x19/0x1b
> > > [    1.776561]  [<ffffffff8113a980>] warn_alloc_failed+0xf0/0x160
> > > [    1.783076]  [<ffffffff810bc28a>] ? on_each_cpu_mask+0x2a/0x60
> > > [    1.789581]  [<ffffffff8113e92f>] __alloc_pages_nodemask+0x7ff/0xa00
> > > [    1.796672]  [<ffffffff815ada2c>] vmemmap_alloc_block+0x62/0xba
> > > [    1.803274]  [<ffffffff815ada99>] vmemmap_alloc_block_buf+0x15/0x3b
> > > [    1.810263]  [<ffffffff815ab8a6>] vmemmap_populate+0xb4/0x21b
> > > [    1.816673]  [<ffffffff815adecd>] sparse_mem_map_populate+0x27/0x35
> > > [    1.823665]  [<ffffffff815ad8bf>] sparse_add_one_section+0x7a/0x185
> > > [    1.830659]  [<ffffffff8159b74f>] __add_pages+0xaf/0x240
> > > [    1.836588]  [<ffffffff81047359>] arch_add_memory+0x59/0xd0
> > > [    1.842804]  [<ffffffff8159ba89>] add_memory+0xb9/0x1b0
> > > [    1.848638]  [<ffffffff8132dd2c>] acpi_memory_device_add+0x18d/0x26d
> > > [    1.855728]  [<ffffffff81303b91>] acpi_bus_device_attach+0x7d/0xcd
> > > [    1.862625]  [<ffffffff8131d92d>] acpi_ns_walk_namespace+0xc8/0x17f
> > > [    1.869616]  [<ffffffff81303b14>] ? acpi_bus_type_and_status+0x90/0x90
> > > [    1.876896]  [<ffffffff81303b14>] ? acpi_bus_type_and_status+0x90/0x90
> > > [    1.884177]  [<ffffffff8131de1c>] acpi_walk_namespace+0x95/0xc5
> > > [    1.890780]  [<ffffffff81304866>] acpi_bus_scan+0x8b/0x9d
> > > [    1.896805]  [<ffffffff81a14a15>] acpi_scan_init+0x63/0x160
> > > [    1.903021]  [<ffffffff81a14830>] acpi_init+0x25d/0x2a6
> > 
> > So basically acpi thinks that some memory block is a hot plug memory
> > and tries to add it. And that consumes lots of memory and we don't have
> > that memory in second kernel.
> 
> That's not exactly the case.  What seems to happen is that there is an ACPI
> memory object in the ACPI namespace and the ACPI memory hotplug driver
> attempts to bind to it.  That driver attempts to find removable memory blocks
> associated with that object and to add them to the memory map.
> 
> Why don't you simply append acpi=off to the kexec command line?  That should
> make the problem go away.

I think we need to initialize acpi because we rely on it for other tables
and things. In fact everything in second kernel re-initializes so why ACPI
should be an exception? We want second kernel boot path to be as close
as possible to first kernel so that chances of successful boot are higher.

So I don't think turning off acpi is way to go here.

Key question is, whey this memory is still being considered as hotplugged
memory while nothing has been hotplugged. I think acpi should not treat
this memory as hotplug memory. And if ACPI does not have a way to figure
it out, then disable memory hotplug functionality makes sense to me.

Thanks
Vivek
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