Re: [PATCH 1/10] memory-hotplug : check whether memory is offline ornot when removing memory

[KOSAKI Motohiro]

On Thu, Oct 4, 2012 at 10:25 PM, Yasuaki Ishimatsu
<isimatu.yasuaki@xxxxxxxxxxxxxx> wrote:
> When calling remove_memory(), the memory should be offline. If the function
> is used to online memory, kernel panic may occur.
>
> So the patch checks whether memory is offline or not.

You don't explain WHY we need the check.


> CC: David Rientjes <rientjes@xxxxxxxxxx>
> CC: Jiang Liu <liuj97@xxxxxxxxx>
> CC: Len Brown <len.brown@xxxxxxxxx>
> CC: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
>
> ---
>  drivers/base/memory.c  |   39 +++++++++++++++++++++++++++++++++++++++
>  include/linux/memory.h |    5 +++++
>  mm/memory_hotplug.c    |   17 +++++++++++++++--
>  3 files changed, 59 insertions(+), 2 deletions(-)
>
> Index: linux-3.6/drivers/base/memory.c
> ===================================================================
> --- linux-3.6.orig/drivers/base/memory.c        2012-10-04 14:22:57.000000000 +0900
> +++ linux-3.6/drivers/base/memory.c     2012-10-04 14:45:46.653585860 +0900
> @@ -70,6 +70,45 @@ void unregister_memory_isolate_notifier(
>  }
>  EXPORT_SYMBOL(unregister_memory_isolate_notifier);
>
> +bool is_memblk_offline(unsigned long start, unsigned long size)

Don't use memblk. Usually memblk mean struct numa_meminfo for x86/numa.
Maybe memory_range_offlined() is better.

And, this function don't take struct memory_block, then this file may be no good
place.

And you need to write down function comment.


> +{
> +       struct memory_block *mem = NULL;
> +       struct mem_section *section;
> +       unsigned long start_pfn, end_pfn;
> +       unsigned long pfn, section_nr;
> +
> +       start_pfn = PFN_DOWN(start);
> +       end_pfn = PFN_UP(start + size);
> +
> +       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;
> +               if (mem->state == MEM_OFFLINE)
> +                       continue;
> +
> +               kobject_put(&mem->dev.kobj);
> +               return false;
> +       }
> +
> +       if (mem)
> +               kobject_put(&mem->dev.kobj);
> +
> +       return true;
> +}
> +EXPORT_SYMBOL(is_memblk_offline);
> +
>  /*
>   * register_memory - Setup a sysfs device for a memory block
>   */
> Index: linux-3.6/include/linux/memory.h
> ===================================================================
> --- linux-3.6.orig/include/linux/memory.h       2012-10-02 18:00:22.000000000 +0900
> +++ linux-3.6/include/linux/memory.h    2012-10-04 14:44:40.902581028 +0900
> @@ -106,6 +106,10 @@ static inline int memory_isolate_notify(
>  {
>         return 0;
>  }
> +static inline bool is_memblk_offline(unsigned long start, unsigned long size)
> +{
> +       return false;
> +}
>  #else
>  extern int register_memory_notifier(struct notifier_block *nb);
>  extern void unregister_memory_notifier(struct notifier_block *nb);
> @@ -120,6 +124,7 @@ extern int memory_isolate_notify(unsigne
>  extern struct memory_block *find_memory_block_hinted(struct mem_section *,
>                                                         struct memory_block *);
>  extern struct memory_block *find_memory_block(struct mem_section *);
> +extern bool is_memblk_offline(unsigned long start, unsigned long size);
>  #define CONFIG_MEM_BLOCK_SIZE  (PAGES_PER_SECTION<<PAGE_SHIFT)
>  enum mem_add_context { BOOT, HOTPLUG };
>  #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
> Index: linux-3.6/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.6.orig/mm/memory_hotplug.c  2012-10-04 14:31:08.000000000 +0900
> +++ linux-3.6/mm/memory_hotplug.c       2012-10-04 14:58:22.449687986 +0900
> @@ -1045,8 +1045,21 @@ int offline_memory(u64 start, u64 size)
>
>  int remove_memory(int nid, u64 start, u64 size)
>  {

Your remove_memory() don't remove anything. that's strange.


> -       /* It is not implemented yet*/
> -       return 0;
> +       int ret = 0;
> +       lock_memory_hotplug();
> +       /*
> +        * The memory might become online by other task, even if you offine it.
> +        * So we check whether the memory has been onlined or not.
> +        */
> +       if (!is_memblk_offline(start, size)) {
> +               pr_warn("memory removing [mem %#010llx-%#010llx] failed, "
> +                       "because the memmory range is online\n",
> +                       start, start + size);

No good warning. You should output which memory block can't be
offlined, I think.


> +               ret = -EAGAIN;
> +       }
> +
> +       unlock_memory_hotplug();
> +       return ret;
>  }
>  EXPORT_SYMBOL_GPL(remove_memory);
>  #else
>
> --
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