* [PATCH] mm/hugetlb.c: check the failure case for find_vma
@ 2019-07-25 1:39 Navid Emamdoost
2019-07-25 17:53 ` Mike Kravetz
0 siblings, 1 reply; 2+ messages in thread
From: Navid Emamdoost @ 2019-07-25 1:39 UTC (permalink / raw)
To: emamd001
Cc: kjlu, smccaman, Navid Emamdoost, Mike Kravetz, linux-mm, linux-kernel
find_vma may fail and return NULL. The null check is added.
Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
---
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);
+
struct address_space *mapping = vma->vm_file->f_mapping;
pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
vma->vm_pgoff;
--
2.17.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] mm/hugetlb.c: check the failure case for find_vma
2019-07-25 1:39 [PATCH] mm/hugetlb.c: check the failure case for find_vma Navid Emamdoost
@ 2019-07-25 17:53 ` Mike Kravetz
0 siblings, 0 replies; 2+ messages in thread
From: Mike Kravetz @ 2019-07-25 17:53 UTC (permalink / raw)
To: Navid Emamdoost, emamd001; +Cc: kjlu, smccaman, linux-mm, linux-kernel
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@gmail.com>
> ---
> 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;
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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