Re: [PATCH v2 2/5] mm: memory_hotplug: Remove assumption on memory state before hotremove

[joeyli <jlee@suse.com>]

Hi Andrea, 

On Fri, Nov 24, 2017 at 10:22:35AM +0000, Andrea Reale wrote:
> Resending the patch adding linux-acpi in CC, as suggested by Rafael.
> Everyone else: apologies for the noise.
> 
> Commit 242831eb15a0 ("Memory hotplug / ACPI: Simplify memory removal")
> introduced an assumption whereas when control
> reaches remove_memory the corresponding memory has been already
> offlined. In that case, the acpi_memhotplug was making sure that
> the assumption held.
> This assumption, however, is not necessarily true if offlining
> and removal are not done by the same "controller" (for example,
> when first offlining via sysfs).
> 
> Removing this assumption for the generic remove_memory code
> and moving it in the specific acpi_memhotplug code. This is
> a dependency for the software-aided arm64 offlining and removal
> process.
> 
> Signed-off-by: Andrea Reale <ar@linux.vnet.ibm.com>
> Signed-off-by: Maciej Bielski <m.bielski@linux.vnet.ibm.com>
> ---
>  drivers/acpi/acpi_memhotplug.c |  2 +-
>  include/linux/memory_hotplug.h |  9 ++++++---
>  mm/memory_hotplug.c            | 13 +++++++++----
>  3 files changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
> index 6b0d3ef..b0126a0 100644
> --- a/drivers/acpi/acpi_memhotplug.c
> +++ b/drivers/acpi/acpi_memhotplug.c
> @@ -282,7 +282,7 @@ static void acpi_memory_remove_memory(struct acpi_memory_device *mem_device)
>  			nid = memory_add_physaddr_to_nid(info->start_addr);
>  
>  		acpi_unbind_memory_blocks(info);
> -		remove_memory(nid, info->start_addr, info->length);
> +		BUG_ON(remove_memory(nid, info->start_addr, info->length));
>  		list_del(&info->list);
>  		kfree(info);
>  	}
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 58e110a..1a9c7b2 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -295,7 +295,7 @@ static inline bool movable_node_is_enabled(void)
>  extern bool is_mem_section_removable(unsigned long pfn, unsigned long nr_pages);
>  extern void try_offline_node(int nid);
>  extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
> -extern void remove_memory(int nid, u64 start, u64 size);
> +extern int remove_memory(int nid, u64 start, u64 size);
>  
>  #else
>  static inline bool is_mem_section_removable(unsigned long pfn,
> @@ -311,7 +311,10 @@ static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>  	return -EINVAL;
>  }
>  
> -static inline void remove_memory(int nid, u64 start, u64 size) {}
> +static inline int remove_memory(int nid, u64 start, u64 size)
> +{
> +	return -EINVAL;
> +}
>  #endif /* CONFIG_MEMORY_HOTREMOVE */
>  
>  extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
> @@ -323,7 +326,7 @@ extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
>  		unsigned long nr_pages);
>  extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
>  extern bool is_memblock_offlined(struct memory_block *mem);
> -extern void remove_memory(int nid, u64 start, u64 size);
> +extern int remove_memory(int nid, u64 start, u64 size);
>  extern int sparse_add_one_section(struct pglist_data *pgdat, unsigned long start_pfn);
>  extern void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
>  		unsigned long map_offset);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index d4b5f29..d5f15af 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1892,7 +1892,7 @@ EXPORT_SYMBOL(try_offline_node);
>   * and online/offline operations before this call, as required by
>   * try_offline_node().
>   */
> -void __ref remove_memory(int nid, u64 start, u64 size)
> +int __ref remove_memory(int nid, u64 start, u64 size)
>  {
>  	int ret;
>  
> @@ -1908,18 +1908,23 @@ void __ref remove_memory(int nid, u64 start, u64 size)
>  	ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL,
>  				check_memblock_offlined_cb);
>  	if (ret)
> -		BUG();
> +		goto end_remove;
> +
> +	ret = arch_remove_memory(start, size);
> +
> +	if (ret)
> +		goto end_remove;

The original code triggers BUG() when any memblock is not offlined. Why
the new logic includes the result of arch_remove_memory()?

But I agreed the we don't need BUG(). Returning a error is better.

>  
>  	/* remove memmap entry */
>  	firmware_map_remove(start, start + size, "System RAM");
>  	memblock_free(start, size);
>  	memblock_remove(start, size);
>  
> -	arch_remove_memory(start, size);
> -
>  	try_offline_node(nid);
>  
> +end_remove:
>  	mem_hotplug_done();
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(remove_memory);
>  #endif /* CONFIG_MEMORY_HOTREMOVE */
> -- 
> 2.7.4
> 
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