[09/15] hugetlb: fix hugetlb cgroup refcounting during mremap

Commit Message

Andrew Morton Nov. 20, 2021, 12:43 a.m. UTC

From: Bui Quang Minh <[e-mail]>
Subject: hugetlb: fix hugetlb cgroup refcounting during mremap

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()

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 550a7d60bd5e35 ("mm, hugepages: add mremap() support for hugepage backed vma")
Signed-off-by: Bui Quang Minh <[e-mail]>
Reviewed-by: Mike Kravetz <[e-mail]>
Reviewed-by: Mina Almasry <[e-mail]>
Cc: Miaohe Lin <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Muchun Song <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/hugetlb_cgroup.h |   12 ++++++++++++
 mm/hugetlb.c                   |    4 +++-
 2 files changed, 15 insertions(+), 1 deletion(-)

Patch

--- a/include/linux/hugetlb_cgroup.h~hugetlb-fix-hugetlb-cgroup-refcounting-during-mremap
+++ a/include/linux/hugetlb_cgroup.h
@@ -128,6 +128,13 @@  static inline void resv_map_dup_hugetlb_
 		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,
@@ -210,6 +217,11 @@  static inline void resv_map_dup_hugetlb_
 						struct resv_map *resv_map)
 {
 }
+
+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)
--- a/mm/hugetlb.c~hugetlb-fix-hugetlb-cgroup-refcounting-during-mremap
+++ a/mm/hugetlb.c
@@ -1037,8 +1037,10 @@  void clear_vma_resv_huge_pages(struct vm
 	 */
 	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);
 }