linux-kernel - [PATCH v2 1/3] mm: update the memmap stat before page is freed

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Message-ID: <20240807211929.3433304-2-pasha.tatashin@soleen.com>
Date: Wed,  7 Aug 2024 21:19:27 +0000
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	cerasuolodomenico@...il.com,
	hannes@...xchg.org,
	j.granados@...sung.com,
	lizhijian@...itsu.com,
	muchun.song@...ux.dev,
	nphamcs@...il.com,
	pasha.tatashin@...een.com,
	rientjes@...gle.com,
	rppt@...nel.org,
	souravpanda@...gle.com,
	vbabka@...e.cz,
	willy@...radead.org
Subject: [PATCH v2 1/3] mm: update the memmap stat before page is freed

It is more logical to update the stat before the page is freed, to avoid
use after free scenarios.

Fixes: 15995a352474 ("mm: report per-page metadata information")
Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Reviewed-by: David Hildenbrand <david@...hat.com>
---
 mm/hugetlb_vmemmap.c | 4 ++--
 mm/page_ext.c        | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 829112b0a914..fa83a7b38199 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -185,11 +185,11 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
 static inline void free_vmemmap_page(struct page *page)
 {
 	if (PageReserved(page)) {
-		free_bootmem_page(page);
 		mod_node_page_state(page_pgdat(page), NR_MEMMAP_BOOT, -1);
+		free_bootmem_page(page);
 	} else {
-		__free_page(page);
 		mod_node_page_state(page_pgdat(page), NR_MEMMAP, -1);
+		__free_page(page);
 	}
 }
 
diff --git a/mm/page_ext.c b/mm/page_ext.c
index c191e490c401..962d45eee1f8 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -330,18 +330,18 @@ static void free_page_ext(void *addr)
 	if (is_vmalloc_addr(addr)) {
 		page = vmalloc_to_page(addr);
 		pgdat = page_pgdat(page);
+		mod_node_page_state(pgdat, NR_MEMMAP,
+				    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
 		vfree(addr);
 	} else {
 		page = virt_to_page(addr);
 		pgdat = page_pgdat(page);
+		mod_node_page_state(pgdat, NR_MEMMAP,
+				    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
 		BUG_ON(PageReserved(page));
 		kmemleak_free(addr);
 		free_pages_exact(addr, table_size);
 	}
-
-	mod_node_page_state(pgdat, NR_MEMMAP,
-			    -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
-
 }
 
 static void __free_page_ext(unsigned long pfn)
-- 
2.46.0.76.ge559c4bf1a-goog