Re: [PATCH 3.2 099/125] mm: fix crashes from mbind() merging vmas

[Hugh Dickins]

On Tue, 8 Jul 2014, Ben Hutchings wrote:

> 3.2.61-rc1 review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Hugh Dickins <hughd@xxxxxxxxxx>
> 
> commit d05f0cdcbe6388723f1900c549b4850360545201 upstream.
> 
> In v2.6.34 commit 9d8cebd4bcd7 ("mm: fix mbind vma merge problem")
> introduced vma merging to mbind(), but it should have also changed the
> convention of passing start vma from queue_pages_range() (formerly
> check_range()) to new_vma_page(): vma merging may have already freed
> that structure, resulting in BUG at mm/mempolicy.c:1738 and probably
> worse crashes.
> 
> Fixes: 9d8cebd4bcd7 ("mm: fix mbind vma merge problem")
> Reported-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Tested-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Acked-by: Christoph Lameter <cl@xxxxxxxxx>
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> [bwh: Backported to 3.2:
>  - Adjust context
>  - Keep the same arguments to migrate_pages() except for private=start]
> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> ---
>  mm/mempolicy.c | 46 ++++++++++++++++++++--------------------------
>  1 file changed, 20 insertions(+), 26 deletions(-)
> 
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -566,24 +566,23 @@ static inline int check_pgd_range(struct
>   * If pagelist != NULL then isolate pages from the LRU and
>   * put them on the pagelist.
>   */
> -static struct vm_area_struct *
> +static int
>  check_range(struct mm_struct *mm, unsigned long start, unsigned long end,
>  		const nodemask_t *nodes, unsigned long flags, void *private)
>  {
> -	int err;
> -	struct vm_area_struct *first, *vma, *prev;
> -
> +	int err = 0;
> +	struct vm_area_struct *vma, *prev;
>  
> -	first = find_vma(mm, start);
> -	if (!first)
> -		return ERR_PTR(-EFAULT);
> +	vma = find_vma(mm, start);
> +	if (!vma)
> +		return -EFAULT;
>  	prev = NULL;
> -	for (vma = first; vma && vma->vm_start < end; vma = vma->vm_next) {
> +	for (; vma && vma->vm_start < end; vma = vma->vm_next) {
>  		if (!(flags & MPOL_MF_DISCONTIG_OK)) {
>  			if (!vma->vm_next && vma->vm_end < end)
> -				return ERR_PTR(-EFAULT);
> +				return -EFAULT;
>  			if (prev && prev->vm_end < vma->vm_start)
> -				return ERR_PTR(-EFAULT);
> +				return -EFAULT;
>  		}
>  		if (!is_vm_hugetlb_page(vma) &&
>  		    ((flags & MPOL_MF_STRICT) ||
> @@ -597,14 +596,12 @@ check_range(struct mm_struct *mm, unsign
>  				start = vma->vm_start;
>  			err = check_pgd_range(vma, start, endvma, nodes,
>  						flags, private);
> -			if (err) {
> -				first = ERR_PTR(err);
> +			if (err)
>  				break;
> -			}
>  		}
>  		prev = vma;
>  	}
> -	return first;
> +	return err;
>  }
>  
>  /*
> @@ -1060,16 +1057,17 @@ out:
>  
>  /*
>   * Allocate a new page for page migration based on vma policy.
> - * Start assuming that page is mapped by vma pointed to by @private.
> + * Start by assuming the page is mapped by the same vma as contains @start.
>   * Search forward from there, if not.  N.B., this assumes that the
>   * list of pages handed to migrate_pages()--which is how we get here--
>   * is in virtual address order.
>   */
> -static struct page *new_vma_page(struct page *page, unsigned long private, int **x)
> +static struct page *new_page(struct page *page, unsigned long start, int **x)
>  {
> -	struct vm_area_struct *vma = (struct vm_area_struct *)private;
> +	struct vm_area_struct *vma;
>  	unsigned long uninitialized_var(address);
>  
> +	vma = find_vma(current->mm, start);
>  	while (vma) {
>  		address = page_address_in_vma(page, vma);
>  		if (address != -EFAULT)
> @@ -1095,7 +1093,7 @@ int do_migrate_pages(struct mm_struct *m
>  	return -ENOSYS;
>  }
>  
> -static struct page *new_vma_page(struct page *page, unsigned long private, int **x)
> +static struct page *new_page(struct page *page, unsigned long start, int **x)
>  {
>  	return NULL;
>  }
> @@ -1105,7 +1103,6 @@ static long do_mbind(unsigned long start
>  		     unsigned short mode, unsigned short mode_flags,
>  		     nodemask_t *nmask, unsigned long flags)
>  {
> -	struct vm_area_struct *vma;
>  	struct mm_struct *mm = current->mm;
>  	struct mempolicy *new;
>  	unsigned long end;
> @@ -1169,19 +1166,16 @@ static long do_mbind(unsigned long start
>  	if (err)
>  		goto mpol_out;
>  
> -	vma = check_range(mm, start, end, nmask,
> +	err = check_range(mm, start, end, nmask,
>  			  flags | MPOL_MF_INVERT, &pagelist);
> -
> -	err = PTR_ERR(vma);
> -	if (!IS_ERR(vma)) {
> +	if (!err) {
>  		int nr_failed = 0;
>  
>  		err = mbind_range(mm, start, end, new);
>  
>  		if (!list_empty(&pagelist)) {
> -			nr_failed = migrate_pages(&pagelist, new_vma_page,
> -						(unsigned long)vma,
> -						false, true);
> +			nr_failed = migrate_pages(&pagelist, new_page,
> +						start, false, true);
>  			if (nr_failed)
>  				putback_lru_pages(&pagelist);
>  		}

I don't think that's correct, I can't see a change to the
"vma = check_range(" in migrate_to_node() which 3.2 and 3.4 trees have.
Does it build (without warning) with CONFIG_NUMA and CONFIG_MIGRATION?
I expect this version I sent yesterday for 3.4.98 will be good for 3.2:

------------------ version for 3.4.98 ------------------