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

[Rafael J. Wysocki]

On 11/23/2017 12:14 PM, Andrea Reale wrote:

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 <a...@linux.vnet.ibm.com>
Signed-off-by: Maciej Bielski <m.biel...@linux.vnet.ibm.com>

Please resend this with a CC to linux-acpi.

Thanks!

---
  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;

/* 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 */