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

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Date:	Wed, 22 Oct 2014 13:02:11 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.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()

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>

-Toshi



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