Commit 356ea386 authored by andrew.yang's avatar andrew.yang Committed by Linus Torvalds
Browse files

mm/migrate: fix race between lock page and clear PG_Isolated 

When memory is tight, system may start to compact memory for large
continuous memory demands.  If one process tries to lock a memory page
that is being locked and isolated for compaction, it may wait a long time
or even forever.  This is because compaction will perform non-atomic
PG_Isolated clear while holding page lock, this may overwrite PG_waiters
set by the process that can't obtain the page lock and add itself to the
waiting queue to wait for the lock to be unlocked.

  CPU1                            CPU2
  lock_page(page); (successful)
                                  lock_page(); (failed)
  __ClearPageIsolated(page);      SetPageWaiters(page) (may be overwritten)
  unlock_page(page);

The solution is to not perform non-atomic operation on page flags while
holding page lock.

Link: https://lkml.kernel.org/r/20220315030515.20263-1-andrew.yang@mediatek.com


Signed-off-by: default avatarandrew.yang <andrew.yang@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Vlastimil Babka" <vbabka@suse.cz>
Cc: David Howells <dhowells@redhat.com>
Cc: "William Kucharski" <william.kucharski@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Nicholas Tang <nicholas.tang@mediatek.com>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent fc89213a

include/linux/page-flags.h

+1 −1
Original line number Diff line number Diff line
@@ -1000,7 +1000,7 @@ PAGE_TYPE_OPS(Guard, guard) 


extern bool is_free_buddy_page(struct page *page);



__PAGEFLAG(Isolated, isolated, PF_ANY);

PAGEFLAG(Isolated, isolated, PF_ANY);



#ifdef CONFIG_MMU

#define __PG_MLOCKED		(1UL << PG_mlocked)

mm/migrate.c

+6 −6
Original line number Diff line number Diff line
@@ -107,7 +107,7 @@ int isolate_movable_page(struct page *page, isolate_mode_t mode) 


	/* Driver shouldn't use PG_isolated bit of page->flags */

	WARN_ON_ONCE(PageIsolated(page));

	__SetPageIsolated(page);

	SetPageIsolated(page);

	unlock_page(page);



	return 0;
@@ -126,7 +126,7 @@ static void putback_movable_page(struct page *page) 


	mapping = page_mapping(page);

	mapping->a_ops->putback_page(page);

	__ClearPageIsolated(page);

	ClearPageIsolated(page);

}



/*
@@ -159,7 +159,7 @@ void putback_movable_pages(struct list_head *l) 
			if (PageMovable(page))

				putback_movable_page(page);

			else

				__ClearPageIsolated(page);

				ClearPageIsolated(page);

			unlock_page(page);

			put_page(page);

		} else {
@@ -883,7 +883,7 @@ static int move_to_new_page(struct page *newpage, struct page *page, 
		VM_BUG_ON_PAGE(!PageIsolated(page), page);

		if (!PageMovable(page)) {

			rc = MIGRATEPAGE_SUCCESS;

			__ClearPageIsolated(page);

			ClearPageIsolated(page);

			goto out;

		}
@@ -905,7 +905,7 @@ static int move_to_new_page(struct page *newpage, struct page *page, 
			 * We clear PG_movable under page_lock so any compactor

			 * cannot try to migrate this page.

			 */

			__ClearPageIsolated(page);

			ClearPageIsolated(page);

		}



		/*
@@ -1091,7 +1091,7 @@ static int unmap_and_move(new_page_t get_new_page, 
		if (unlikely(__PageMovable(page))) {

			lock_page(page);

			if (!PageMovable(page))

				__ClearPageIsolated(page);

				ClearPageIsolated(page);

			unlock_page(page);

		}

		goto out;