Re: [PATCH 5/5] mm/memory-hotplug: Rework unregister_mem_sect_under_nodes

[Jonathan Cameron]

On Mon, 15 Oct 2018 17:30:34 +0200
Oscar Salvador <osalvador@xxxxxxxxxxxxxxxxxx> wrote:

> From: Oscar Salvador <osalvador@xxxxxxx>
> 
> This tries to address another issue about accessing
> unitiliazed pages.
> 
> Jonathan reported a problem [1] where we can access steal pages
> in case we hot-remove memory without onlining it first.
> 
> This time is in unregister_mem_sect_under_nodes.
> This function tries to get the nid from the pfn and then
> tries to remove the symlink between mem_blk <-> nid and vice versa.
> 
> Since we already know the nid in remove_memory(), we can pass
> it down the chain to unregister_mem_sect_under_nodes.
> There we can just remove the symlinks without the need
> to look into the pages.
> 
> [1] https://www.spinics.net/lists/linux-mm/msg161316.html
> 
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>

Hi Oscar,

I've not gone through these in detail, but I have run some
quick smoke tests and all seems fine with the out of tree arm64
patches we are carrying (with the obvious changes to match
up with those for other architectures that you make in this set).

Tested-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

In particular (as expected) it fixes the issue you mention above
so I can drop the hack I had in place to avoid that :)

Thanks,

Jonathan

> ---
>  drivers/base/memory.c  |  9 ++++-----
>  drivers/base/node.c    | 38 +++++++-------------------------------
>  include/linux/memory.h |  2 +-
>  include/linux/node.h   |  9 ++++-----
>  mm/memory_hotplug.c    |  2 +-
>  5 files changed, 17 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 0e5985682642..3d8c65d84bea 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -744,8 +744,7 @@ unregister_memory(struct memory_block *memory)
>  	device_unregister(&memory->dev);
>  }
>  
> -static int remove_memory_section(unsigned long node_id,
> -			       struct mem_section *section, int phys_device)
> +static int remove_memory_section(unsigned long nid, struct mem_section *section)
>  {
>  	struct memory_block *mem;
>  
> @@ -759,7 +758,7 @@ static int remove_memory_section(unsigned long node_id,
>  	if (!mem)
>  		goto out_unlock;
>  
> -	unregister_mem_sect_under_nodes(mem, __section_nr(section));
> +	unregister_mem_sect_under_nodes(nid, mem);
>  
>  	mem->section_count--;
>  	if (mem->section_count == 0)
> @@ -772,12 +771,12 @@ static int remove_memory_section(unsigned long node_id,
>  	return 0;
>  }
>  
> -int unregister_memory_section(struct mem_section *section)
> +int unregister_memory_section(int nid, struct mem_section *section)
>  {
>  	if (!present_section(section))
>  		return -EINVAL;
>  
> -	return remove_memory_section(0, section, 0);
> +	return remove_memory_section(nid, section);
>  }
>  #endif /* CONFIG_MEMORY_HOTREMOVE */
>  
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 86d6cd92ce3d..65bc5920bd3d 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -453,40 +453,16 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
>  	return 0;
>  }
>  
> -/* unregister memory section under all nodes that it spans */
> -int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
> -				    unsigned long phys_index)
> +/*
> + * This mem_blk is going to be removed, so let us remove the link
> + * to the node and vice versa
> + */
> +void unregister_mem_sect_under_nodes(int nid, struct memory_block *mem_blk)
>  {
> -	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
> -	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);
> -
> -	sect_start_pfn = section_nr_to_pfn(phys_index);
> -	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
> -	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
> -		int nid;
> -
> -		nid = get_nid_for_pfn(pfn);
> -		if (nid < 0)
> -			continue;
> -		if (!node_online(nid))
> -			continue;
> -		if (node_test_and_set(nid, *unlinked_nodes))
> -			continue;
> -		sysfs_remove_link(&node_devices[nid]->dev.kobj,
> +	sysfs_remove_link(&node_devices[nid]->dev.kobj,
>  			 kobject_name(&mem_blk->dev.kobj));
> -		sysfs_remove_link(&mem_blk->dev.kobj,
> +	sysfs_remove_link(&mem_blk->dev.kobj,
>  			 kobject_name(&node_devices[nid]->dev.kobj));
> -	}
> -	NODEMASK_FREE(unlinked_nodes);
> -	return 0;
>  }
>  
>  int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
> diff --git a/include/linux/memory.h b/include/linux/memory.h
> index a6ddefc60517..d75ec88ca09d 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(int nid, struct mem_section *section);
>  #ifdef CONFIG_MEMORY_HOTREMOVE
> -extern int unregister_memory_section(struct mem_section *);
> +extern int unregister_memory_section(int nid, struct mem_section *);
>  #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 257bb3d6d014..dddead9937ab 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -72,8 +72,8 @@ 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 void unregister_mem_sect_under_nodes(int nid,
> +						struct memory_block *mem_blk);
>  
>  #ifdef CONFIG_HUGETLBFS
>  extern void register_hugetlbfs_with_node(node_registration_func_t doregister,
> @@ -105,10 +105,9 @@ 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 void unregister_mem_sect_under_nodes(int nid,
> +						struct memory_block *mem_blk)
>  {
> -	return 0;
>  }
>  
>  static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6b98321aa52f..66ccbb5b8a88 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -528,7 +528,7 @@ static int __remove_section(int nid, struct mem_section *ms,
>  	if (!valid_section(ms))
>  		return ret;
>  
> -	ret = unregister_memory_section(ms);
> +	ret = unregister_memory_section(nid, ms);
>  	if (ret)
>  		return ret;
>