[PATCH 3/3] mm/debug: Check page poisoned firstly in dump_page()

[Kefeng Wang]

If page is poisoned, it will crash when we call some page related
functions, so must check whether the page is poisoned or not firstly.

Fixes: 6197ab984b41 ("mm: improve dump_page() for compound pages")
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 mm/debug.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c
index 84cdcd0f7bd3..cf84cd9df527 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -44,20 +44,19 @@ const struct trace_print_flags vmaflag_names[] = {
 
 static void __dump_page(struct page *page, const char *reason)
 {
-	struct page *head = compound_head(page);
+	struct page *head = NULL;
 	struct address_space *mapping;
-	bool page_poisoned = PagePoisoned(page);
-	bool compound = PageCompound(page);
+	bool compound;
 	/*
 	 * Accessing the pageblock without the zone lock. It could change to
 	 * "isolate" again in the meantime, but since we are just dumping the
 	 * state for debugging, it should be fine to accept a bit of
 	 * inaccuracy here due to racing.
 	 */
-	bool page_cma = is_migrate_cma_page(page);
+	bool page_cma;
 	int mapcount;
 	char *type = "";
-
+	bool page_poisoned = PagePoisoned(page);
 	/*
 	 * If struct page is poisoned don't access Page*() functions as that
 	 * leads to recursive loop. Page*() check for poisoned pages, and calls
@@ -68,6 +67,10 @@ static void __dump_page(struct page *page, const char *reason)
 		goto hex_only;
 	}
 
+	head = compound_head(page);
+	page_poisoned = PagePoisoned(page);
+	page_cma = is_migrate_cma_page(page);
+
 	if (page < head || (page >= head + MAX_ORDER_NR_PAGES)) {
 		/*
 		 * Corrupt page, so we cannot call page_mapping. Instead, do a
@@ -178,7 +181,7 @@ static void __dump_page(struct page *page, const char *reason)
 	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
 			sizeof(unsigned long), page,
 			sizeof(struct page), false);
-	if (head != page)
+	if (head && head != page)
 		print_hex_dump(KERN_WARNING, "head: ", DUMP_PREFIX_NONE, 32,
 			sizeof(unsigned long), head,
 			sizeof(struct page), false);
-- 
2.26.2