Hi Mike,
Thanks for your detailed explanation. I see that for huge_pte_alloc the address is checked to be within vma.
Best regards,
On Thu, Jul 25, 2019 at 12:53 PM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
On 7/24/19 6:39 PM, Navid Emamdoost wrote:
> find_vma may fail and return NULL. The null check is added.
>
> Signed-off-by: Navid Emamdoost <navid.emamdoost@xxxxxxxxx>
> ---
> mm/hugetlb.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ede7e7f5d1ab..9c5e8b7a6476 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4743,6 +4743,9 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
> pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
> {
> struct vm_area_struct *vma = find_vma(mm, addr);
> + if (!vma)
> + return (pte_t *)pmd_alloc(mm, pud, addr);
> +
Hello Navid,
You should not mix declarations and code like this. I am surprised that your
compiler did not issue a warning such as:
mm/hugetlb.c: In function ‘huge_pmd_share’:
mm/hugetlb.c:4815:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
struct address_space *mapping = vma->vm_file->f_mapping;
^~~~~~
While it is true that the routine find_vma can return NULL. I do not
believe it is possible here within the context of huge_pmd_share. Why?
huge_pmd_share is called from huge_pte_alloc to allocate a page table
entry for a huge page. So, the calling code is attempting to populate
page tables. There are three callers of huge_pte_alloc: hugetlb_fault,
copy_hugetlb_page_range and __mcopy_atomic_hugetlb. In each of these
routines (or their callers) it has been verified that address is within
a vma. In addition, mmap_sem is held so that vmas can not change.
Therefore, there should be no way for find_vma to return NULL here.
Please let me know if there is something I have overlooked. Otherwise,
there is no need for such a modification.
--
Mike Kravetz
> struct address_space *mapping = vma->vm_file->f_mapping;
> pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
> vma->vm_pgoff;
>
Navid.
