2021-03-22 17:53:10

by Peter Xu

Subject: [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

When uffd-minor enabled, we need to put the page cache before handling the
userfault in hugetlb_no_page(), otherwise the page refcount got leaked.

This can be reproduced by running userfaultfd selftest with hugetlb_shared
mode, then cat /proc/meminfo.

Cc: Axel Rasmussen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Andrew Morton <[email protected]>
Fixes: f2bf15fb0969 ("userfaultfd: add minor fault registration mode")
Signed-off-by: Peter Xu <[email protected]>
---
mm/hugetlb.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 408dbc08298a..56b78a206913 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4449,6 +4449,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
/* Check for page in userfault range. */
if (userfaultfd_minor(vma)) {
unlock_page(page);
+ put_page(page);
ret = hugetlb_handle_userfault(vma, mapping, idx,
flags, haddr,
VM_UFFD_MINOR);
--
2.26.2

2021-03-22 20:15:28

by Mike Kravetz

Subject: Re: [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

On 3/22/21 10:51 AM, Peter Xu wrote:
> When uffd-minor enabled, we need to put the page cache before handling the
> userfault in hugetlb_no_page(), otherwise the page refcount got leaked.
>
> This can be reproduced by running userfaultfd selftest with hugetlb_shared
> mode, then cat /proc/meminfo.
>
> Cc: Axel Rasmussen <[email protected]>
> Cc: Andrea Arcangeli <[email protected]>
> Cc: Mike Kravetz <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Fixes: f2bf15fb0969 ("userfaultfd: add minor fault registration mode")
> Signed-off-by: Peter Xu <[email protected]>
> ---
> mm/hugetlb.c | 1 +
> 1 file changed, 1 insertion(+)

Thanks for finding/fixing.

Reviewed-by: Mike Kravetz <[email protected]>

I think this is just in Andrew's tree. So it will need to be fixed
there.
--
Mike Kravetz

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 408dbc08298a..56b78a206913 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4449,6 +4449,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> /* Check for page in userfault range. */
> if (userfaultfd_minor(vma)) {
> unlock_page(page);
> + put_page(page);
> ret = hugetlb_handle_userfault(vma, mapping, idx,
> flags, haddr,
> VM_UFFD_MINOR);
>

2021-03-22 20:21:57

by Axel Rasmussen

Subject: Re: [PATCH] userfaultfd/hugetlbfs: Fix minor fault page leak

On Mon, Mar 22, 2021 at 10:51 AM Peter Xu <[email protected]> wrote:
>
> When uffd-minor enabled, we need to put the page cache before handling the
> userfault in hugetlb_no_page(), otherwise the page refcount got leaked.
>
> This can be reproduced by running userfaultfd selftest with hugetlb_shared
> mode, then cat /proc/meminfo.
>
> Cc: Axel Rasmussen <[email protected]>
> Cc: Andrea Arcangeli <[email protected]>
> Cc: Mike Kravetz <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Fixes: f2bf15fb0969 ("userfaultfd: add minor fault registration mode")
> Signed-off-by: Peter Xu <[email protected]>
> ---
> mm/hugetlb.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 408dbc08298a..56b78a206913 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4449,6 +4449,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> /* Check for page in userfault range. */
> if (userfaultfd_minor(vma)) {
> unlock_page(page);
> + put_page(page);
> ret = hugetlb_handle_userfault(vma, mapping, idx,
> flags, haddr,
> VM_UFFD_MINOR);
> --
> 2.26.2
>

Thanks for the fix, Peter! I applied the patch and verified it does
indeed fix the issue.

Reviewed-by: Axel Rasmussen <[email protected]>