Re: [v6 05/15] mm: don't accessed uninitialized struct pages

[Michal Hocko]

On Mon 07-08-17 16:38:39, Pavel Tatashin wrote:
> In deferred_init_memmap() where all deferred struct pages are initialized
> we have a check like this:
> 
>     if (page->flags) {
>             VM_BUG_ON(page_zone(page) != zone);
>             goto free_range;
>     }
> 
> This way we are checking if the current deferred page has already been
> initialized. It works, because memory for struct pages has been zeroed, and
> the only way flags are not zero if it went through __init_single_page()
> before.  But, once we change the current behavior and won't zero the memory
> in memblock allocator, we cannot trust anything inside "struct page"es
> until they are initialized. This patch fixes this.
> 
> This patch defines a new accessor memblock_get_reserved_pfn_range()
> which returns successive ranges of reserved PFNs.  deferred_init_memmap()
> calls it to determine if a PFN and its struct page has already been
> initialized.

Why don't we simply check the pfn against pgdat->first_deferred_pfn?

> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx>
> ---
>  include/linux/memblock.h |  3 +++
>  mm/memblock.c            | 54 ++++++++++++++++++++++++++++++++++++++++++------
>  mm/page_alloc.c          | 11 +++++++++-
>  3 files changed, 61 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index bae11c7e7bf3..b6a2a610f5e1 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -320,6 +320,9 @@ int memblock_is_map_memory(phys_addr_t addr);
>  int memblock_is_region_memory(phys_addr_t base, phys_addr_t size);
>  bool memblock_is_reserved(phys_addr_t addr);
>  bool memblock_is_region_reserved(phys_addr_t base, phys_addr_t size);
> +void memblock_get_reserved_pfn_range(unsigned long pfn,
> +				     unsigned long *pfn_start,
> +				     unsigned long *pfn_end);
>  
>  extern void __memblock_dump_all(void);
>  
> diff --git a/mm/memblock.c b/mm/memblock.c
> index bf14aea6ab70..08f449acfdd1 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1580,7 +1580,13 @@ void __init memblock_mem_limit_remove_map(phys_addr_t limit)
>  	memblock_cap_memory_range(0, max_addr);
>  }
>  
> -static int __init_memblock memblock_search(struct memblock_type *type, phys_addr_t addr)
> +/**
> + * Return index in regions array if addr is within the region. Otherwise
> + * return -1. If -1 is returned and *next_idx is not %NULL, sets it to the
> + * next region index or -1 if there is none.
> + */
> +static int __init_memblock memblock_search(struct memblock_type *type,
> +					   phys_addr_t addr, int *next_idx)
>  {
>  	unsigned int left = 0, right = type->cnt;
>  
> @@ -1595,22 +1601,26 @@ static int __init_memblock memblock_search(struct memblock_type *type, phys_addr
>  		else
>  			return mid;
>  	} while (left < right);
> +
> +	if (next_idx)
> +		*next_idx = (right == type->cnt) ? -1 : right;
> +
>  	return -1;
>  }
>  
>  bool __init memblock_is_reserved(phys_addr_t addr)
>  {
> -	return memblock_search(&memblock.reserved, addr) != -1;
> +	return memblock_search(&memblock.reserved, addr, NULL) != -1;
>  }
>  
>  bool __init_memblock memblock_is_memory(phys_addr_t addr)
>  {
> -	return memblock_search(&memblock.memory, addr) != -1;
> +	return memblock_search(&memblock.memory, addr, NULL) != -1;
>  }
>  
>  int __init_memblock memblock_is_map_memory(phys_addr_t addr)
>  {
> -	int i = memblock_search(&memblock.memory, addr);
> +	int i = memblock_search(&memblock.memory, addr, NULL);
>  
>  	if (i == -1)
>  		return false;
> @@ -1622,7 +1632,7 @@ int __init_memblock memblock_search_pfn_nid(unsigned long pfn,
>  			 unsigned long *start_pfn, unsigned long *end_pfn)
>  {
>  	struct memblock_type *type = &memblock.memory;
> -	int mid = memblock_search(type, PFN_PHYS(pfn));
> +	int mid = memblock_search(type, PFN_PHYS(pfn), NULL);
>  
>  	if (mid == -1)
>  		return -1;
> @@ -1646,7 +1656,7 @@ int __init_memblock memblock_search_pfn_nid(unsigned long pfn,
>   */
>  int __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size)
>  {
> -	int idx = memblock_search(&memblock.memory, base);
> +	int idx = memblock_search(&memblock.memory, base, NULL);
>  	phys_addr_t end = base + memblock_cap_size(base, &size);
>  
>  	if (idx == -1)
> @@ -1655,6 +1665,38 @@ int __init_memblock memblock_is_region_memory(phys_addr_t base, phys_addr_t size
>  		 memblock.memory.regions[idx].size) >= end;
>  }
>  
> +/**
> + * memblock_get_reserved_pfn_range - search for the next reserved region
> + *
> + * @pfn: start searching from this pfn.
> + *
> + * RETURNS:
> + * [start_pfn, end_pfn), where start_pfn >= pfn. If none is found
> + * start_pfn, and end_pfn are both set to ULONG_MAX.
> + */
> +void __init_memblock memblock_get_reserved_pfn_range(unsigned long pfn,
> +						     unsigned long *start_pfn,
> +						     unsigned long *end_pfn)
> +{
> +	struct memblock_type *type = &memblock.reserved;
> +	int next_idx, idx;
> +
> +	idx = memblock_search(type, PFN_PHYS(pfn), &next_idx);
> +	if (idx == -1 && next_idx == -1) {
> +		*start_pfn = ULONG_MAX;
> +		*end_pfn = ULONG_MAX;
> +		return;
> +	}
> +
> +	if (idx == -1) {
> +		idx = next_idx;
> +		*start_pfn = PFN_DOWN(type->regions[idx].base);
> +	} else {
> +		*start_pfn = pfn;
> +	}
> +	*end_pfn = PFN_DOWN(type->regions[idx].base + type->regions[idx].size);
> +}
> +
>  /**
>   * memblock_is_region_reserved - check if a region intersects reserved memory
>   * @base: base of region to check
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 63d16c185736..983de0a8047b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1447,6 +1447,7 @@ static int __init deferred_init_memmap(void *data)
>  	pg_data_t *pgdat = data;
>  	int nid = pgdat->node_id;
>  	struct mminit_pfnnid_cache nid_init_state = { };
> +	unsigned long resv_start_pfn = 0, resv_end_pfn = 0;
>  	unsigned long start = jiffies;
>  	unsigned long nr_pages = 0;
>  	unsigned long walk_start, walk_end;
> @@ -1491,6 +1492,10 @@ static int __init deferred_init_memmap(void *data)
>  			pfn = zone->zone_start_pfn;
>  
>  		for (; pfn < end_pfn; pfn++) {
> +			if (pfn >= resv_end_pfn)
> +				memblock_get_reserved_pfn_range(pfn,
> +								&resv_start_pfn,
> +								&resv_end_pfn);
>  			if (!pfn_valid_within(pfn))
>  				goto free_range;
>  
> @@ -1524,7 +1529,11 @@ static int __init deferred_init_memmap(void *data)
>  				cond_resched();
>  			}
>  
> -			if (page->flags) {
> +			/*
> +			 * Check if this page has already been initialized due
> +			 * to being reserved during boot in memblock.
> +			 */
> +			if (pfn >= resv_start_pfn) {
>  				VM_BUG_ON(page_zone(page) != zone);
>  				goto free_range;
>  			}
> -- 
> 2.14.0

-- 
Michal Hocko
SUSE Labs