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