[147/262] mm/page_isolation: guard against possible putback unisolated page

Commit Message

Andrew Morton Nov. 5, 2021, 8:42 p.m. UTC

From: Miaohe Lin <[e-mail]>
Subject: mm/page_isolation: guard against possible putback unisolated page

Isolating a free page in an isolated pageblock is expected to always work
as watermarks don't apply here.  But if __isolate_free_page() failed, due
to condition changes, the page will be left on the free list.  And the
page will be put back to free list again via __putback_isolated_page(). 
This may trigger VM_BUG_ON_PAGE() on page->flags checking in
__free_one_page() if PageReported is set.  Or we will corrupt the free
list because list_add() will be called for pages already on another list. 
Add a VM_WARN_ON() to complain about this change.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
Signed-off-by: Miaohe Lin <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_isolation.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Patch

--- a/mm/page_isolation.c~mm-page_isolation-guard-against-possible-putback-unisolated-page
+++ a/mm/page_isolation.c
@@ -94,8 +94,13 @@  static void unset_migratetype_isolate(st
 			buddy = page + (buddy_pfn - pfn);
 
 			if (!is_migrate_isolate_page(buddy)) {
-				__isolate_free_page(page, order);
-				isolated_page = true;
+				isolated_page = !!__isolate_free_page(page, order);
+				/*
+				 * Isolating a free page in an isolated pageblock
+				 * is expected to always work as watermarks don't
+				 * apply here.
+				 */
+				VM_WARN_ON(!isolated_page);
 			}
 		}
 	}