Re: [Patch v4 02/12] memory-hotplug: check whether all memory blocks are offlined or not when removing memory

[Tang Chen <tangchen@cn.fujitsu.com>]

On 11/27/2012 06:00 PM, Wen Congyang wrote:
> From: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
>
> We remove the memory like this:
> 1. lock memory hotplug
> 2. offline a memory block
> 3. unlock memory hotplug
> 4. repeat 1-3 to offline all memory blocks
> 5. lock memory hotplug
> 6. remove memory(TODO)
> 7. unlock memory hotplug
>
> All memory blocks must be offlined before removing memory. But we don't hold
> the lock in the whole operation. So we should check whether all memory blocks
> are offlined before step6. Otherwise, kernel maybe panicked.
>
> CC: David Rientjes<rientjes@google.com>
> CC: Jiang Liu<liuj97@gmail.com>
> CC: Len Brown<len.brown@intel.com>
> CC: Christoph Lameter<cl@linux.com>
> Cc: Minchan Kim<minchan.kim@gmail.com>
> CC: Andrew Morton<akpm@linux-foundation.org>
> CC: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
> Signed-off-by: Wen Congyang<wency@cn.fujitsu.com>
> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>

Reviewed-by: Tang Chen <tangchen@cn.fujitsu.com>

> ---
>   drivers/base/memory.c          |  6 ++++++
>   include/linux/memory_hotplug.h |  1 +
>   mm/memory_hotplug.c            | 47 ++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 54 insertions(+)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 86c8821..badb025 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -675,6 +675,12 @@ int offline_memory_block(struct memory_block *mem)
>   	return ret;
>   }
>
> +/* return true if the memory block is offlined, otherwise, return false */
> +bool is_memblock_offlined(struct memory_block *mem)
> +{
> +	return mem->state == MEM_OFFLINE;
> +}
> +
>   /*
>    * Initialize the sysfs support for memory devices...
>    */
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 95573ec..38675e9 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -236,6 +236,7 @@ extern int add_memory(int nid, u64 start, u64 size);
>   extern int arch_add_memory(int nid, u64 start, u64 size);
>   extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
>   extern int offline_memory_block(struct memory_block *mem);
> +extern bool is_memblock_offlined(struct memory_block *mem);
>   extern int remove_memory(u64 start, u64 size);
>   extern int sparse_add_one_section(struct zone *zone, unsigned long start_pfn,
>   								int nr_pages);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b825dbc..b6d1101 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1054,6 +1054,53 @@ repeat:
>   		goto repeat;
>   	}
>
> +	lock_memory_hotplug();
> +
> +	/*
> +	 * we have offlined all memory blocks like this:
> +	 *   1. lock memory hotplug
> +	 *   2. offline a memory block
> +	 *   3. unlock memory hotplug
> +	 *
> +	 * repeat step1-3 to offline the memory block. All memory blocks
> +	 * must be offlined before removing memory. But we don't hold the
> +	 * lock in the whole operation. So we should check whether all
> +	 * memory blocks are offlined.
> +	 */
> +
> +	for (pfn = start_pfn; pfn<  end_pfn; pfn += PAGES_PER_SECTION) {
> +		section_nr = pfn_to_section_nr(pfn);
> +		if (!present_section_nr(section_nr))
> +			continue;
> +
> +		section = __nr_to_section(section_nr);
> +		/* same memblock? */
> +		if (mem)
> +			if ((section_nr>= mem->start_section_nr)&&
> +			    (section_nr<= mem->end_section_nr))
> +				continue;
> +
> +		mem = find_memory_block_hinted(section, mem);
> +		if (!mem)
> +			continue;
> +
> +		ret = is_memblock_offlined(mem);
> +		if (!ret) {
> +			pr_warn("removing memory fails, because memory "
> +				"[%#010llx-%#010llx] is onlined\n",
> +				PFN_PHYS(section_nr_to_pfn(mem->start_section_nr)),
> +				PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1)) - 1);
> +
> +			kobject_put(&mem->dev.kobj);
> +			unlock_memory_hotplug();
> +			return ret;
> +		}
> +	}
> +
> +	if (mem)
> +		kobject_put(&mem->dev.kobj);
> +	unlock_memory_hotplug();
> +
>   	return 0;
>   }
>   #else