Commit b653db77 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle)
Browse files

mm: Clear page->private when splitting or migrating a page 



In our efforts to remove uses of PG_private, we have found folios with
the private flag clear and folio->private not-NULL.  That is the root
cause behind 642d51fb ("ceph: check folio PG_private bit instead
of folio->private").  It can also affect a few other filesystems that
haven't yet reported a problem.

compaction_alloc() can return a page with uninitialised page->private,
and rather than checking all the callers of migrate_pages(), just zero
page->private after calling get_new_page().  Similarly, the tail pages
from split_huge_page() may also have an uninitialised page->private.

Reported-by: default avatarXiubo Li <xiubli@redhat.com>
Tested-by: default avatarXiubo Li <xiubli@redhat.com>
Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
parent cb995f4e

mm/huge_memory.c

+1 −0
Original line number Diff line number Diff line
@@ -2377,6 +2377,7 @@ static void __split_huge_page_tail(struct page *head, int tail, 
			page_tail);

	page_tail->mapping = head->mapping;

	page_tail->index = head->index + tail;

	page_tail->private = 0;



	/* Page flags must be visible before we make the page non-compound. */

	smp_wmb();

mm/migrate.c

+1 −0
Original line number Diff line number Diff line
@@ -1106,6 +1106,7 @@ static int unmap_and_move(new_page_t get_new_page, 
	if (!newpage)

		return -ENOMEM;



	newpage->private = 0;

	rc = __unmap_and_move(page, newpage, force, mode);

	if (rc == MIGRATEPAGE_SUCCESS)

		set_page_owner_migrate_reason(newpage, reason);