[PATCH v6 20/37] mm: fix non-compound multi-order memory accounting in __free_pages

Suren Baghdasaryan
2024-03-21T16:37:54Z

When a non-compound multi-order page is freed, it is possible that a
speculative reference keeps the page pinned. In this case we free all
pages except for the first page, which will be freed later by the last
put_page(). However the page passed to put_page() is indistinguishable
from an order-0 page, so it cannot do the accounting, just as it cannot
free the subsequent pages. Do the accounting here, where we free the
pages.

Reported-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/pgalloc_tag.h | 24 ++++++++++++++++++++++++
mm/page_alloc.c | 5 ++++-
2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 093edf98c3d7..50d212330bbb 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -96,12 +96,36 @@ static inline void pgalloc_tag_split(struct page *page, unsigned int nr)
page_ext_put(page_ext);
}

+static inline struct alloc_tag *pgalloc_tag_get(struct page *page)
+{
+ struct alloc_tag *tag = NULL;
+
+ if (mem_alloc_profiling_enabled()) {
+ union codetag_ref *ref = get_page_tag_ref(page);
+
+ alloc_tag_sub_check(ref);
+ if (ref && ref->ct)
+ tag = ct_to_alloc_tag(ref->ct);
+ put_page_tag_ref(ref);
+ }
+
+ return tag;
+}
+
+static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
+{
+ if (mem_alloc_profiling_enabled() && tag)
+ this_cpu_sub(tag->counters->bytes, PAGE_SIZE * nr);
+}
+
#else /* CONFIG_MEM_ALLOC_PROFILING */

static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
unsigned int nr) {}
static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}
static inline void pgalloc_tag_split(struct page *page, unsigned int nr) {}
+static inline struct alloc_tag *pgalloc_tag_get(struct page *page) { return NULL; }
+static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) {}

#endif /* CONFIG_MEM_ALLOC_PROFILING */

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fd1cc5b80a56..00e0ae4cbf2d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4700,12 +4700,15 @@ void __free_pages(struct page *page, unsigned int order)
{
/* get PageHead before we drop reference */
int head = PageHead(page);
+ struct alloc_tag *tag = pgalloc_tag_get(page);

if (put_page_testzero(page))
free_the_page(page, order);
- else if (!head)
+ else if (!head) {
+ pgalloc_tag_sub_pages(tag, (1 << order) - 1);
while (order-- > 0)
free_the_page(page + (1 << order), order);
+ }
}
EXPORT_SYMBOL(__free_pages);

--
2.44.0.291.gc1ea87d7ee-goog