[PATCH mm v2] mm, kasan: fix for "integrate page_alloc init with HW_TAGS"

[Andrey Konovalov]

My commit "integrate page_alloc init with HW_TAGS" changed the order of
kernel_unpoison_pages() and kernel_init_free_pages() calls. This leads
to complaints from the page unpoisoning code, as the poison pattern gets
overwritten for __GFP_ZERO allocations.

Fix by restoring the initial order. Also add a warning comment.

Reported-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 mm/page_alloc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 033bd92e8398..d2c020563c0b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2328,6 +2328,13 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 	arch_alloc_page(page, order);
 	debug_pagealloc_map_pages(page, 1 << order);
 
+	/*
+	 * Page unpoisoning must happen before memory initialization.
+	 * Otherwise, the poison pattern will be overwritten for __GFP_ZERO
+	 * allocations and the page unpoisoning code will complain.
+	 */
+	kernel_unpoison_pages(page, 1 << order);
+
 	/*
 	 * As memory initialization might be integrated into KASAN,
 	 * kasan_alloc_pages and kernel_init_free_pages must be
@@ -2338,7 +2345,6 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
 	if (init && !kasan_has_integrated_init())
 		kernel_init_free_pages(page, 1 << order);
 
-	kernel_unpoison_pages(page, 1 << order);
 	set_page_owner(page, order, gfp_flags);
 }
 
-- 
2.31.0.291.g576ba9dcdaf-goog