[PATCH] hugetlb: fix hugetlb cgroup refcounting during mremap

[PATCH] hugetlb: fix hugetlb cgroup refcounting during mremap

[Bui Quang Minh]

When hugetlb_vm_op_open() is called during copy_vma(), we may take the
reference to resv_map->css. Later, when clearing the reservation pointer
of old_vma after transferring it to new_vma, we forget to drop the
reference to resv_map->css. This leads to a reference leak of css.

Fixes this by adding a check to drop reservation css  reference in
clear_vma_resv_huge_pages()

Fixes: 550a7d6 (mm, hugepages: add mremap() support for hugepage backed vma)
Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
---
 include/linux/hugetlb_cgroup.h | 12 ++++++++++++
 mm/hugetlb.c                   |  4 +++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
index c137396129db..ba025ae27882 100644
--- a/include/linux/hugetlb_cgroup.h
+++ b/include/linux/hugetlb_cgroup.h
@@ -128,6 +128,13 @@ static inline void resv_map_dup_hugetlb_cgroup_uncharge_info(
 		css_get(resv_map->css);
 }
 
+static inline void resv_map_put_hugetlb_cgroup_uncharge_info(
+						struct resv_map *resv_map)
+{
+	if (resv_map->css)
+		css_put(resv_map->css);
+}
+
 extern int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
 					struct hugetlb_cgroup **ptr);
 extern int hugetlb_cgroup_charge_cgroup_rsvd(int idx, unsigned long nr_pages,
@@ -211,6 +218,11 @@ static inline void resv_map_dup_hugetlb_cgroup_uncharge_info(
 {
 }
 
+static inline void resv_map_put_hugetlb_cgroup_uncharge_info(
+						struct resv_map *resv_map)
+{
+}
+
 static inline int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
 					       struct hugetlb_cgroup **ptr)
 {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e09159c957e3..3a2479003ddf 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1037,8 +1037,10 @@ void clear_vma_resv_huge_pages(struct vm_area_struct *vma)
 	 */
 	struct resv_map *reservations = vma_resv_map(vma);
 
-	if (reservations && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
+	if (reservations && is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
+		resv_map_put_hugetlb_cgroup_uncharge_info(reservations);
 		kref_put(&reservations->refs, resv_map_release);
+	}
 
 	reset_vma_resv_huge_pages(vma);
 }
-- 
2.25.1

Re: [PATCH] hugetlb: fix hugetlb cgroup refcounting during mremap

[Andrew Morton]

On Sat, 13 Nov 2021 22:44:10 +0700 Bui Quang Minh <minhquangbui99@gmail.com> wrote:

> When hugetlb_vm_op_open() is called during copy_vma(), we may take the
> reference to resv_map->css. Later, when clearing the reservation pointer
> of old_vma after transferring it to new_vma, we forget to drop the
> reference to resv_map->css. This leads to a reference leak of css.
> 
> Fixes this by adding a check to drop reservation css  reference in
> clear_vma_resv_huge_pages()

Thanks.  I added cc:stable to this (550a7d60bd5e35a was merged a year
ago) and I've queued it for 5.16-rc2, pending suitable reviewer feedback.

Re: [PATCH] hugetlb: fix hugetlb cgroup refcounting during mremap

[Mina Almasry]

On Mon, Nov 15, 2021 at 1:16 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Sat, 13 Nov 2021 22:44:10 +0700 Bui Quang Minh <minhquangbui99@gmail.com> wrote:
>
> > When hugetlb_vm_op_open() is called during copy_vma(), we may take the
> > reference to resv_map->css. Later, when clearing the reservation pointer
> > of old_vma after transferring it to new_vma, we forget to drop the
> > reference to resv_map->css. This leads to a reference leak of css.
> >
> > Fixes this by adding a check to drop reservation css  reference in
> > clear_vma_resv_huge_pages()
>
> Thanks.  I added cc:stable to this (550a7d60bd5e35a was merged a year
> ago) and I've queued it for 5.16-rc2, pending suitable reviewer feedback.
>

Thanks,

Reviewed-by: Mina Almasry <almasrymina@google.com>

Re: [PATCH] hugetlb: fix hugetlb cgroup refcounting during mremap

[Mike Kravetz]

Subject:   Re: [PATCH] hugetlb: fix hugetlb cgroup refcounting during mremap

To:        Andrew Morton <akpm@linux-foundation.org>, Bui Quang Minh <minhquangbui99@gmail.com>

Cc:        Miaohe Lin <linmiaohe@huawei.com>, Michal Hocko <mhocko@suse.com>, Muchun Song <songmuchun@bytedance.com>, Mina Almasry <almasrymina@google.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

Bcc:       

-=-=-=-=-=-=-=-=-=# Don't remove this line #=-=-=-=-=-=-=-=-=-

On 11/15/21 1:16 PM, Andrew Morton wrote:

> On Sat, 13 Nov 2021 22:44:10 +0700 Bui Quang Minh <minhquangbui99@gmail.com> wrote:

> 

>> When hugetlb_vm_op_open() is called during copy_vma(), we may take the

>> reference to resv_map->css. Later, when clearing the reservation pointer

>> of old_vma after transferring it to new_vma, we forget to drop the

>> reference to resv_map->css. This leads to a reference leak of css.

>>

>> Fixes this by adding a check to drop reservation css  reference in

>> clear_vma_resv_huge_pages()



Good catch!  Sorry I missed this in my review.



Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com



> Thanks.  I added cc:stable to this (550a7d60bd5e35a was merged a year

> ago) and I've queued it for 5.16-rc2, pending suitable reviewer feedback.



I may be confused, but 550a7d60bd5e35a was just merged in 5.16-rc1 so

no need for cc:stable.

-- 

Mike Kravetz