Re: [PATCH v2] memory-hotplug: Clear pgdat which is allocated by bootmem in try_offline_node()

[Yasuaki Ishimatsu]

(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@xxxxxxxxxxxxxx>
>
> Thanks for the update. It looks good.

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

Thank you for your  review.

Thanks,
Yasuaki Ishimatasu

> -Toshi


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