A deep process chain with many vmas could grow really high. kref
refcounting interface used in anon_vma_name structure will detect
a counter overflow when it reaches REFCOUNT_SATURATED value but will
only generate a warning about broken refcounting.
To ensure anon_vma_name refcount does not overflow, stop anon_vma_name
sharing when the refcount reaches INT_MAX, which still leaves INT_MAX/2
values before the counter reaches REFCOUNT_SATURATED. This should provide
enough headroom for raising the refcounts temporarily.
Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
include/linux/mm_inline.h | 18 ++++++++++++++----
mm/madvise.c | 3 +--
2 files changed, 15 insertions(+), 6 deletions(-)
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 70b619442d56..b189e2638843 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -156,15 +156,25 @@ static inline void anon_vma_name_get(struct anon_vma_name *anon_name)
extern void anon_vma_name_put(struct anon_vma_name *anon_name);
+static inline
+struct anon_vma_name *anon_vma_name_reuse(struct anon_vma_name *anon_name)
+{
+ /* Prevent anon_name refcount saturation early on */
+ if (kref_read(&anon_name->kref) < INT_MAX) {
+ anon_vma_name_get(anon_name);
+ return anon_name;
+
+ }
+ return anon_vma_name_alloc(anon_name->name);
+}
+
static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma,
struct vm_area_struct *new_vma)
{
struct anon_vma_name *anon_name = vma_anon_name(orig_vma);
- if (anon_name) {
- anon_vma_name_get(anon_name);
- new_vma->anon_name = anon_name;
- }
+ if (anon_name)
+ new_vma->anon_name = anon_vma_name_reuse(anon_name);
}
static inline void free_vma_anon_name(struct vm_area_struct *vma)
diff --git a/mm/madvise.c b/mm/madvise.c
index f81d62d8ce9b..a395884aeecb 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -122,8 +122,7 @@ static int replace_vma_anon_name(struct vm_area_struct *vma,
if (anon_vma_name_eq(orig_name, anon_name))
return 0;
- anon_vma_name_get(anon_name);
- vma->anon_name = anon_name;
+ vma->anon_name = anon_vma_name_reuse(anon_name);
anon_vma_name_put(orig_name);
return 0;
--
2.35.1.473.g83b2b277ed-goog
