Subject: Re: [PATCH v5 02/14] memory-hotplug: check whether all memory blocks are offlined or not when removing memory

From: Kamezawa Hiroyuki <[email-masked]>
Date: Wed, 26 Dec 2012 12:10:43 +0900

(2012/12/24 21:09), Tang Chen wrote:
> From: Yasuaki Ishimatsu <[email-masked]>
> 
> 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.
> 
> Signed-off-by: Wen Congyang <[email-masked]>
> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>

Acked-by: KAMEZAWA Hiroyuki <[email-masked]>

a nitpick below.

> ---
>   drivers/base/memory.c          |    6 +++++
>   include/linux/memory_hotplug.h |    1 +
>   mm/memory_hotplug.c            |   47 ++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 54 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 987604d..8300a18 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -693,6 +693,12 @@ 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 4a45c4e..8dd0950 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -247,6 +247,7 @@ 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 62e04c9..d43d97b 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1430,6 +1430,53 @@ 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) {

I prefer adding mem = NULL at the start of this for().

> +		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;
> +

Thanks,
-Kame