Subject: Re: [RFC PATCH v3 4/13] memory-hotplug : remove /sys/firmware/memmap/X sysfs

From: Wen Congyang <[email-masked]>
Date: Mon, 16 Jul 2012 10:32:26 +0800

At 07/09/2012 06:26 PM, Yasuaki Ishimatsu Wrote:
> When (hot)adding memory into system, /sys/firmware/memmap/X/{end, start, type}
> sysfs files are created. But there is no code to remove these files. The patch
> implements the function to remove them.
> 
> Note : The code does not free firmware_map_entry since there is no way to free
>        memory which is allocated by bootmem.
> 
> CC: David Rientjes <[email-masked]>
> CC: Jiang Liu <[email-masked]>
> CC: Len Brown <[email-masked]>
> CC: Benjamin Herrenschmidt <[email-masked]>
> CC: Paul Mackerras <[email-masked]>
> CC: Christoph Lameter <[email-masked]>
> Cc: Minchan Kim <[email-masked]>
> CC: Andrew Morton <[email-masked]>
> CC: KOSAKI Motohiro <[email-masked]>
> CC: Wen Congyang <[email-masked]>
> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
> 
> ---
>  drivers/firmware/memmap.c    |   78 ++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/firmware-map.h |    6 +++
>  mm/memory_hotplug.c          |    6 ++-
>  3 files changed, 88 insertions(+), 2 deletions(-)
> 
> Index: linux-3.5-rc6/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.5-rc6.orig/mm/memory_hotplug.c	2012-07-09 18:23:13.323844923 +0900
> +++ linux-3.5-rc6/mm/memory_hotplug.c	2012-07-09 18:23:19.522767424 +0900
> @@ -661,7 +661,11 @@ EXPORT_SYMBOL_GPL(add_memory);
> 
>  int remove_memory(int nid, u64 start, u64 size)
>  {
> -	return -EBUSY;
> +	lock_memory_hotplug();
> +	/* remove memmap entry */
> +	firmware_map_remove(start, start + size - 1, "System RAM");
> +	unlock_memory_hotplug();
> +	return 0;
> 
>  }
>  EXPORT_SYMBOL_GPL(remove_memory);
> Index: linux-3.5-rc6/include/linux/firmware-map.h
> ===================================================================
> --- linux-3.5-rc6.orig/include/linux/firmware-map.h	2012-07-09 18:23:09.532892314 +0900
> +++ linux-3.5-rc6/include/linux/firmware-map.h	2012-07-09 18:23:19.523767412 +0900
> @@ -25,6 +25,7 @@
> 
>  int firmware_map_add_early(u64 start, u64 end, const char *type);
>  int firmware_map_add_hotplug(u64 start, u64 end, const char *type);
> +int firmware_map_remove(u64 start, u64 end, const char *type);
> 
>  #else /* CONFIG_FIRMWARE_MEMMAP */
> 
> @@ -38,6 +39,11 @@ static inline int firmware_map_add_hotpl
>  	return 0;
>  }
> 
> +static inline int firmware_map_remove(u64 start, u64 end, const char *type)
> +{
> +	return 0;
> +}
> +
>  #endif /* CONFIG_FIRMWARE_MEMMAP */
> 
>  #endif /* _LINUX_FIRMWARE_MAP_H */
> Index: linux-3.5-rc6/drivers/firmware/memmap.c
> ===================================================================
> --- linux-3.5-rc6.orig/drivers/firmware/memmap.c	2012-07-09 18:23:09.532892314 +0900
> +++ linux-3.5-rc6/drivers/firmware/memmap.c	2012-07-09 18:25:46.371931554 +0900
> @@ -21,6 +21,7 @@
>  #include <linux/types.h>
>  #include <linux/bootmem.h>
>  #include <linux/slab.h>
> +#include <linux/mm.h>
> 
>  /*
>   * Data types ------------------------------------------------------------------
> @@ -79,7 +80,22 @@ static const struct sysfs_ops memmap_att
>  	.show = memmap_attr_show,
>  };
> 
> +#define to_memmap_entry(obj) container_of(obj, struct firmware_map_entry, kobj)
> +
> +static void release_firmware_map_entry(struct kobject *kobj)
> +{
> +	struct firmware_map_entry *entry = to_memmap_entry(kobj);
> +	struct page *head_page;
> +
> +	head_page = virt_to_head_page(entry);
> +	if (PageSlab(head_page))
> +		kfree(entry);
> +
> +	/* There is no way to free memory allocated from bootmem*/
> +}
> +
>  static struct kobj_type memmap_ktype = {
> +	.release	= release_firmware_map_entry,
>  	.sysfs_ops	= &memmap_attr_ops,
>  	.default_attrs	= def_attrs,
>  };
> @@ -123,6 +139,16 @@ static int firmware_map_add_entry(u64 st
>  	return 0;
>  }
> 
> +/**
> + * firmware_map_remove_entry() - Does the real work to remove a firmware
> + * memmap entry.
> + * @entry: removed entry.
> + **/
> +static inline void firmware_map_remove_entry(struct firmware_map_entry *entry)
> +{
> +	list_del(&entry->list);
> +}
> +
>  /*
>   * Add memmap entry on sysfs
>   */
> @@ -144,6 +170,31 @@ static int add_sysfs_fw_map_entry(struct
>  	return 0;
>  }
> 
> +/*
> + * Remove memmap entry on sysfs
> + */
> +static inline void remove_sysfs_fw_map_entry(struct firmware_map_entry *entry)
> +{
> +	kobject_put(&entry->kobj);
> +}
> +
> +/*
> + * Search memmap entry
> + */
> +
> +struct firmware_map_entry * __meminit
> +find_firmware_map_entry(u64 start, u64 end, const char *type)
> +{
> +	struct firmware_map_entry *entry;
> +
> +	list_for_each_entry(entry, &map_entries, list)
> +		if ((entry->start == start) && (entry->end == end) &&
> +		    (!strcmp(entry->type, type)))
> +			return entry;
> +
> +	return NULL;
> +}
> +
>  /**
>   * firmware_map_add_hotplug() - Adds a firmware mapping entry when we do
>   * memory hotplug.
> @@ -196,6 +247,32 @@ int __init firmware_map_add_early(u64 st
>  	return firmware_map_add_entry(start, end, type, entry);
>  }
> 
> +/**
> + * firmware_map_remove() - remove a firmware mapping entry
> + * @start: Start of the memory range.
> + * @end:   End of the memory range (inclusive).
> + * @type:  Type of the memory range.
> + *
> + * removes a firmware mapping entry.
> + *
> + * Returns 0 on success, or -EINVAL if no entry.
> + **/
> +int __meminit firmware_map_remove(u64 start, u64 end, const char *type)
> +{
> +	struct firmware_map_entry *entry;
> +
> +	entry = find_firmware_map_entry(start, end, type);
> +	if (!entry)
> +		return -EINVAL;
> +
> +	/* remove the memmap entry */
> +	remove_sysfs_fw_map_entry(entry);
> +
> +	firmware_map_remove_entry(entry);

You should call firmware_map_remove_entry() before remove_sysfs_fw_map_entry(),
otherwise it will cause kernel panicked(entry may be freed in remove_sysfs_fw_map_entry()).

Thanks
Wen Congyang

> +
> +	return 0;
> +}
> +
>  /*
>   * Sysfs functions -------------------------------------------------------------
>   */
> @@ -218,7 +295,6 @@ static ssize_t type_show(struct firmware
>  }
> 
>  #define to_memmap_attr(_attr) container_of(_attr, struct memmap_attribute, attr)
> -#define to_memmap_entry(obj) container_of(obj, struct firmware_map_entry, kobj)
> 
>  static ssize_t memmap_attr_show(struct kobject *kobj,
>  				struct attribute *attr, char *buf)
> 
>