linux-kernel - Re: [PATCH v2] memory-hotplug: Clear pgdat which is allocated by bootmem in try_offline

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Date:	Thu, 23 Oct 2014 07:45:44 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <zhenzhang.zhang@...wei.com>,
	<wangnan0@...wei.com>, <tangchen@...fujitsu.com>,
	<dave.hansen@...el.com>, <rientjes@...gle.com>
Subject: Re: [PATCH v2] memory-hotplug: Clear pgdat which is allocated by
 bootmem in try_offline_node()

(2014/10/23 4:02), Toshi Kani wrote:
> On Wed, 2014-10-22 at 16:51 +0900, Yasuaki Ishimatsu wrote:
>> When hot adding the same memory after hot removing a memory,
>> the following messages are shown:
>>
>> WARNING: CPU: 20 PID: 6 at mm/page_alloc.c:4968 free_area_init_node+0x3fe/0x426()
>> ...
>> Call Trace:
>>   [<...>] dump_stack+0x46/0x58
>>   [<...>] warn_slowpath_common+0x81/0xa0
>>   [<...>] warn_slowpath_null+0x1a/0x20
>>   [<...>] free_area_init_node+0x3fe/0x426
>>   [<...>] ? up+0x32/0x50
>>   [<...>] hotadd_new_pgdat+0x90/0x110
>>   [<...>] add_memory+0xd4/0x200
>>   [<...>] acpi_memory_device_add+0x1aa/0x289
>>   [<...>] acpi_bus_attach+0xfd/0x204
>>   [<...>] ? device_register+0x1e/0x30
>>   [<...>] acpi_bus_attach+0x178/0x204
>>   [<...>] acpi_bus_scan+0x6a/0x90
>>   [<...>] ? acpi_bus_get_status+0x2d/0x5f
>>   [<...>] acpi_device_hotplug+0xe8/0x418
>>   [<...>] acpi_hotplug_work_fn+0x1f/0x2b
>>   [<...>] process_one_work+0x14e/0x3f0
>>   [<...>] worker_thread+0x11b/0x510
>>   [<...>] ? rescuer_thread+0x350/0x350
>>   [<...>] kthread+0xe1/0x100
>>   [<...>] ? kthread_create_on_node+0x1b0/0x1b0
>>   [<...>] ret_from_fork+0x7c/0xb0
>>   [<...>] ? kthread_create_on_node+0x1b0/0x1b0
>>
>> The detaled explanation is as follows:
>>
>> When hot removing memory, pgdat is set to 0 in try_offline_node().
>> But if the pgdat is allocated by bootmem allocator, the clearing
>> step is skipped. And when hot adding the same memory, the uninitialized
>> pgdat is reused. But free_area_init_node() checks wether pgdat is set
>> to zero. As a result, free_area_init_node() hits WARN_ON().
>>
>> This patch clears pgdat which is allocated by bootmem allocator
>> in try_offline_node().
>>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>
> Thanks for the update. It looks good.
>

> Reviewed-by: Toshi Kani <toshi.kani@...com>

Thank you for your  review.

Thanks,
Yasuaki Ishimatasu

>
> -Toshi
>
>
>


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