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SubjectRe: [PATCH RFC 3/3] mm/memory_hotplug: Remove memory block devices before arch_remove_memory()
On Mon, Apr 08, 2019 at 12:12:26PM +0200, David Hildenbrand wrote:
> Let's factor out removing of memory block devices, which is only
> necessary for memory added via add_memory() and friends that created
> memory block devices. Remove the devices before calling
> arch_remove_memory().
>
> TODO: We should try to get rid of the errors that could be reported by
> unregister_memory_block_under_nodes(). Ignoring failures is not that
> nice.

Hi David,

I am sorry but I will not have to look into this until next week as I am
up to my ears with work plus I am in the middle of a move.

I remember I was once trying to simplify unregister_mem_sect_under_nodes (your
new unregister_memory_block_under_nodes), and I checked whether we could get
rid of the NODEMASK_ALLOC there, something like:

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 8598fcbd2a17..f4294a2928dd 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -805,16 +805,10 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
unsigned long phys_index)
{
- NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
+ nodemask_t unlinked_nodes;
unsigned long pfn, sect_start_pfn, sect_end_pfn;

- if (!mem_blk) {
- NODEMASK_FREE(unlinked_nodes);
- return -EFAULT;
- }
- if (!unlinked_nodes)
- return -ENOMEM;
- nodes_clear(*unlinked_nodes);
+ nodes_clear(unlinked_nodes);

sect_start_pfn = section_nr_to_pfn(phys_index);
sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
@@ -826,14 +820,13 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
continue;
if (!node_online(nid))
continue;
- if (node_test_and_set(nid, *unlinked_nodes))
+ if (node_test_and_set(nid, unlinked_nodes))
continue;
sysfs_remove_link(&node_devices[nid]->dev.kobj,
kobject_name(&mem_blk->dev.kobj));
sysfs_remove_link(&mem_blk->dev.kobj,
kobject_name(&node_devices[nid]->dev.kobj));
}
- NODEMASK_FREE(unlinked_nodes);
return 0;
}

nodemask_t is 128bytes when CONFIG_NODES_SHIFT is 10 , which is the maximum value.
We just need to check whether we can overflow the stack or not.

AFAICS, it is not really a shore stack but it might not be that deep either.

>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> drivers/base/memory.c | 41 +++++++++++++++--------------------------
> drivers/base/node.c | 7 +++----
> include/linux/memory.h | 2 +-
> include/linux/node.h | 6 ++----
> mm/memory_hotplug.c | 10 ++++------
> 5 files changed, 25 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 847b33061e2e..fd8940c37129 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -752,40 +752,29 @@ int hotplug_memory_register(unsigned long start, unsigned long size)
> }
>
> #ifdef CONFIG_MEMORY_HOTREMOVE
> -static int remove_memory_section(struct mem_section *section)
> +void hotplug_memory_unregister(unsigned long start, unsigned long size)
> {
> + unsigned long block_nr_pages = memory_block_size_bytes() >> PAGE_SHIFT;
> + unsigned long start_pfn = PFN_DOWN(start);
> + unsigned long end_pfn = start_pfn + (size >> PAGE_SHIFT);
> struct memory_block *mem;
> + unsigned long pfn;
>
> - mutex_lock(&mem_sysfs_mutex);
> -
> - /*
> - * Some users of the memory hotplug do not want/need memblock to
> - * track all sections. Skip over those.
> - */
> - mem = find_memory_block(section);
> - if (!mem)
> - goto out_unlock;
> -
> - unregister_mem_sect_under_nodes(mem, __section_nr(section));
> + BUG_ON(!IS_ALIGNED(start, memory_block_size_bytes()));
> + BUG_ON(!IS_ALIGNED(size, memory_block_size_bytes()));
>
> - mem->section_count--;
> - if (mem->section_count == 0)
> + mutex_lock(&mem_sysfs_mutex);
> + for (pfn = start_pfn; pfn != end_pfn; pfn += block_nr_pages) {
> + mem = find_memory_block(__pfn_to_section(pfn));
> + if (!mem)
> + continue;
> + mem->section_count = 0;
> + unregister_memory_block_under_nodes(mem);
> unregister_memory(mem);
> - else
> - put_device(&mem->dev);
> -
> -out_unlock:
> + }
> mutex_unlock(&mem_sysfs_mutex);
> - return 0;
> }
>
> -int unregister_memory_section(struct mem_section *section)
> -{
> - if (!present_section(section))
> - return -EINVAL;
> -
> - return remove_memory_section(section);
> -}
> #endif /* CONFIG_MEMORY_HOTREMOVE */
>
> /* return true if the memory block is offlined, otherwise, return false */
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 8598fcbd2a17..f9997770ac15 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -802,8 +802,7 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
> }
>
> /* unregister memory section under all nodes that it spans */
> -int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> - unsigned long phys_index)
> +int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> {
> NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
> unsigned long pfn, sect_start_pfn, sect_end_pfn;
> @@ -816,8 +815,8 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> return -ENOMEM;
> nodes_clear(*unlinked_nodes);
>
> - sect_start_pfn = section_nr_to_pfn(phys_index);
> - sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
> + sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
> + sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
> for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
> int nid;
>
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index e275dc775834..414e43ab0881 100644
> --- a/include/linux/memory.h
> +++ b/include/linux/memory.h
> @@ -113,7 +113,7 @@ extern int register_memory_isolate_notifier(struct notifier_block *nb);
> extern void unregister_memory_isolate_notifier(struct notifier_block *nb);
> int hotplug_memory_register(unsigned long start, unsigned long size);
> #ifdef CONFIG_MEMORY_HOTREMOVE
> -extern int unregister_memory_section(struct mem_section *);
> +void hotplug_memory_unregister(unsigned long start, unsigned long size);
> #endif
> extern int memory_dev_init(void);
> extern int memory_notify(unsigned long val, void *v);
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 1a557c589ecb..02a29e71b175 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -139,8 +139,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid);
> extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
> extern int register_mem_sect_under_node(struct memory_block *mem_blk,
> void *arg);
> -extern int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> - unsigned long phys_index);
> +extern int unregister_memory_block_under_nodes(struct memory_block *mem_blk);
>
> extern int register_memory_node_under_compute_node(unsigned int mem_nid,
> unsigned int cpu_nid,
> @@ -176,8 +175,7 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk,
> {
> return 0;
> }
> -static inline int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> - unsigned long phys_index)
> +static inline int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> {
> return 0;
> }
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 13ee0a26e034..041b93c5eede 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -518,14 +518,9 @@ static int __remove_section(struct zone *zone, struct mem_section *ms,
> {
> unsigned long start_pfn;
> int scn_nr;
> - int ret = -EINVAL;
>
> if (!valid_section(ms))
> - return ret;
> -
> - ret = unregister_memory_section(ms);
> - if (ret)
> - return ret;
> + return -EINVAL;
>
> scn_nr = __section_nr(ms);
> start_pfn = section_nr_to_pfn((unsigned long)scn_nr);
> @@ -1875,6 +1870,9 @@ void __ref __remove_memory(int nid, u64 start, u64 size)
> memblock_free(start, size);
> memblock_remove(start, size);
>
> + /* remove memory block devices before removing memory */
> + hotplug_memory_unregister(start, size);
> +
> arch_remove_memory(nid, start, size, NULL);
>
> try_offline_node(nid);
> --
> 2.17.2
>

--
Oscar Salvador
SUSE L3

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