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

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Date:	Wed, 08 Jan 2014 23:26:43 +0800
From:	Baoquan <bhe@...hat.com>
To:	linux-acpi@...r.kernel.org
CC:	zhangyanfei@...fujitsu.com, tangchen@...fujitsu.com,
	vgoyal@...hat.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, dyoung@...hat.com
Subject: kdump failed because of hotplug memory adding in kdump kernel

Hi,

There's a bug found on intel machine which is numa with hotplug memory.
In this machine, numa is on in 1st kernel, but off in 2nd kernel. when
reserve 512M memory even more memory, kdump always failed. The error log
has been added as attachment, you can check it.

>From log, it can be seen clearly hotplug memory caused this, and we set
the memory_device_handler as null to skip the hotplug memory adding,
kdump is successfull.

Below is personal analysis:
-------------------------
>From ACPI code, In 1st kernel init, bios/efi will detect hardware and
form E820 table, meanwhile ACPI is prepared too. Then E820 is built and
passed to 2nd kernel. However, during initialization, acpi table init
call acpi_os_get_root_pointer(), this function will check whether
acpi_rsdp is ready. If not, it will check whether rsdp can be fetched
from efi. Finally, it will try EBDA or area between E0000 and FFFFF
directly. The 3rd is the case of this bug.  Once rsdp is got ,it will
initialize all ACPI tables, and build namespace tree which includes
hotplug memory ns object. That's why hotplug memory can be found.  So
in acpi_bus_scan trigger the memory_device_handler is matched and
acpi_memory_device_add is called.

Now questions:
1)If acpi tables are handled like acpi_os_get_root_pointer() doing,
acpi regions are passed to 2nd kernel by memmap=xx#yy, but where are
they used?  I can see these regions are added into E820 in kdump kernel.

If acpi regions passed from 1st kernel by memmap=xx#yy are not used, and
acpi is detected always like this, I guess there must be something wrong
with it.

2)if we disable memory hotplug in second kernel and if first kernel
reserved a memory in hotplug memory region, will second kerenl still see
that memroy?

Please help check this.

Baoquan
Thanks

View attachment "error_all.log" of type "text/plain" (71368 bytes)

View attachment "disable-acpi-mem-hotplug-for-exactmap.patch" of type "text/plain" (1508 bytes)