Re: [PATCH v2 1/3] mm/memory_hotplug: add missing mem_hotplug_lock

[Greg KH]

On Mon, Nov 20, 2023 at 11:27:32AM +0100, Sumanth Korikkar wrote:
> >From Documentation/core-api/memory-hotplug.rst:
> When adding/removing/onlining/offlining memory or adding/removing
> heterogeneous/device memory, we should always hold the mem_hotplug_lock
> in write mode to serialise memory hotplug (e.g. access to global/zone
> variables).
> 
> mhp_(de)init_memmap_on_memory() functions can change zone stats and
> struct page content, but they are currently called w/o the
> mem_hotplug_lock.
> 
> When memory block is being offlined and when kmemleak goes through each
> populated zone, the following theoretical race conditions could occur:
> CPU 0:					     | CPU 1:
> memory_offline()			     |
> -> offline_pages()			     |
> 	-> mem_hotplug_begin()		     |
> 	   ...				     |
> 	-> mem_hotplug_done()		     |
> 					     | kmemleak_scan()
> 					     | -> get_online_mems()
> 					     |    ...
> -> mhp_deinit_memmap_on_memory()	     |
>   [not protected by mem_hotplug_begin/done()]|
>   Marks memory section as offline,	     |   Retrieves zone_start_pfn
>   poisons vmemmap struct pages and updates   |   and struct page members.
>   the zone related data			     |
>    					     |    ...
>    					     | -> put_online_mems()
> 
> Fix this by ensuring mem_hotplug_lock is taken before performing
> mhp_init_memmap_on_memory(). Also ensure that
> mhp_deinit_memmap_on_memory() holds the lock.
> 
> online/offline_pages() are currently only called from
> memory_block_online/offline(), so it is safe to move the locking there.
> 
> Fixes: a08a2ae34613 ("mm,memory_hotplug: allocate memmap from the added memory range")
> Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Sumanth Korikkar <sumanthk@xxxxxxxxxxxxx>
> ---
>  drivers/base/memory.c | 18 +++++++++++++++---
>  mm/memory_hotplug.c   | 13 ++++++-------
>  2 files changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index f3b9a4d0fa3b..8a13babd826c 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -180,6 +180,9 @@ static inline unsigned long memblk_nr_poison(struct memory_block *mem)
>  }
>  #endif
>  
> +/*
> + * Must acquire mem_hotplug_lock in write mode.
> + */
>  static int memory_block_online(struct memory_block *mem)
>  {
>  	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
> @@ -204,10 +207,11 @@ static int memory_block_online(struct memory_block *mem)
>  	if (mem->altmap)
>  		nr_vmemmap_pages = mem->altmap->free;
>  
> +	mem_hotplug_begin();
>  	if (nr_vmemmap_pages) {
>  		ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages, zone);
>  		if (ret)
> -			return ret;
> +			goto out;
>  	}
>  
>  	ret = online_pages(start_pfn + nr_vmemmap_pages,
> @@ -215,7 +219,7 @@ static int memory_block_online(struct memory_block *mem)
>  	if (ret) {
>  		if (nr_vmemmap_pages)
>  			mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
> -		return ret;
> +		goto out;
>  	}
>  
>  	/*
> @@ -227,9 +231,14 @@ static int memory_block_online(struct memory_block *mem)
>  					  nr_vmemmap_pages);
>  
>  	mem->zone = zone;
> +out:
> +	mem_hotplug_done();
>  	return ret;
>  }
>  
> +/*
> + * Must acquire mem_hotplug_lock in write mode.
> + */
>  static int memory_block_offline(struct memory_block *mem)
>  {
>  	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
> @@ -247,6 +256,7 @@ static int memory_block_offline(struct memory_block *mem)
>  	if (mem->altmap)
>  		nr_vmemmap_pages = mem->altmap->free;
>  
> +	mem_hotplug_begin();
>  	if (nr_vmemmap_pages)
>  		adjust_present_page_count(pfn_to_page(start_pfn), mem->group,
>  					  -nr_vmemmap_pages);
> @@ -258,13 +268,15 @@ static int memory_block_offline(struct memory_block *mem)
>  		if (nr_vmemmap_pages)
>  			adjust_present_page_count(pfn_to_page(start_pfn),
>  						  mem->group, nr_vmemmap_pages);
> -		return ret;
> +		goto out;
>  	}
>  
>  	if (nr_vmemmap_pages)
>  		mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
>  
>  	mem->zone = NULL;
> +out:
> +	mem_hotplug_done();
>  	return ret;
>  }
>  
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1b03f4ec6fd2..c8238fc5edcb 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1129,6 +1129,9 @@ void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned long nr_pages)
>  	kasan_remove_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
>  }
>  
> +/*
> + * Must be called with mem_hotplug_lock in write mode.
> + */
>  int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  		       struct zone *zone, struct memory_group *group)
>  {
> @@ -1149,7 +1152,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  			 !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
>  		return -EINVAL;
>  
> -	mem_hotplug_begin();
>  
>  	/* associate pfn range with the zone */
>  	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE);
> @@ -1208,7 +1210,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  	writeback_set_ratelimit();
>  
>  	memory_notify(MEM_ONLINE, &arg);
> -	mem_hotplug_done();
>  	return 0;
>  
>  failed_addition:
> @@ -1217,7 +1218,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  		 (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);
>  	memory_notify(MEM_CANCEL_ONLINE, &arg);
>  	remove_pfn_range_from_zone(zone, pfn, nr_pages);
> -	mem_hotplug_done();
>  	return ret;
>  }
>  
> @@ -1863,6 +1863,9 @@ static int count_system_ram_pages_cb(unsigned long start_pfn,
>  	return 0;
>  }
>  
> +/*
> + * Must be called with mem_hotplug_lock in write mode.
> + */
>  int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>  			struct zone *zone, struct memory_group *group)
>  {
> @@ -1885,8 +1888,6 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>  			 !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
>  		return -EINVAL;
>  
> -	mem_hotplug_begin();
> -
>  	/*
>  	 * Don't allow to offline memory blocks that contain holes.
>  	 * Consequently, memory blocks with holes can never get onlined
> @@ -2027,7 +2028,6 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>  
>  	memory_notify(MEM_OFFLINE, &arg);
>  	remove_pfn_range_from_zone(zone, start_pfn, nr_pages);
> -	mem_hotplug_done();
>  	return 0;
>  
>  failed_removal_isolated:
> @@ -2042,7 +2042,6 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>  		 (unsigned long long) start_pfn << PAGE_SHIFT,
>  		 ((unsigned long long) end_pfn << PAGE_SHIFT) - 1,
>  		 reason);
> -	mem_hotplug_done();
>  	return ret;
>  }
>  
> -- 
> 2.41.0
> 

Hi,

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