Commit 8b881763 authored by Vlastimil Babka's avatar Vlastimil Babka
Browse files

mm/migrate: make isolate_movable_page() skip slab pages 

In the next commit we want to rearrange struct slab fields to allow a larger
rcu_head. Afterwards, the page->mapping field will overlap with SLUB's "struct
list_head slab_list", where the value of prev pointer can become LIST_POISON2,
which is 0x122 + POISON_POINTER_DELTA.  Unfortunately the bit 1 being set can
confuse PageMovable() to be a false positive and cause a GPF as reported by lkp
[1].

To fix this, make isolate_movable_page() skip pages with the PageSlab flag set.
This is a bit tricky as we need to add memory barriers to SLAB and SLUB's page
allocation and freeing, and their counterparts to isolate_movable_page().

Based on my RFC from [2]. Added a comment update from Matthew's variant in [3]
and, as done there, moved the PageSlab checks to happen before trying to take
the page lock.

[1] https://lore.kernel.org/all/208c1757-5edd-fd42-67d4-1940cc43b50f@intel.com/
[2] https://lore.kernel.org/all/aec59f53-0e53-1736-5932-25407125d4d4@suse.cz/
[3] https://lore.kernel.org/all/YzsVM8eToHUeTP75@casper.infradead.org/



Reported-by: default avatarkernel test robot <yujie.liu@intel.com>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarHyeonggon Yoo <42.hyeyoo@gmail.com>
parent bc29d5bd

mm/migrate.c

+12 −3
Original line number Diff line number Diff line
@@ -74,13 +74,22 @@ int isolate_movable_page(struct page *page, isolate_mode_t mode) 
	if (unlikely(!get_page_unless_zero(page)))

		goto out;



	if (unlikely(PageSlab(page)))

		goto out_putpage;

	/* Pairs with smp_wmb() in slab freeing, e.g. SLUB's __free_slab() */

	smp_rmb();

	/*

	 * Check PageMovable before holding a PG_lock because page's owner

	 * assumes anybody doesn't touch PG_lock of newly allocated page

	 * so unconditionally grabbing the lock ruins page's owner side.

	 * Check movable flag before taking the page lock because

	 * we use non-atomic bitops on newly allocated page flags so

	 * unconditionally grabbing the lock ruins page's owner side.

	 */

	if (unlikely(!__PageMovable(page)))

		goto out_putpage;

	/* Pairs with smp_wmb() in slab allocation, e.g. SLUB's alloc_slab_page() */

	smp_rmb();

	if (unlikely(PageSlab(page)))

		goto out_putpage;



	/*

	 * As movable pages are not isolated from LRU lists, concurrent

	 * compaction threads can race against page migration functions

mm/slab.c

+5 −1
Original line number Diff line number Diff line
@@ -1370,6 +1370,8 @@ static struct slab *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, 


	account_slab(slab, cachep->gfporder, cachep, flags);

	__folio_set_slab(folio);

	/* Make the flag visible before any changes to folio->mapping */

	smp_wmb();

	/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */

	if (sk_memalloc_socks() && page_is_pfmemalloc(folio_page(folio, 0)))

		slab_set_pfmemalloc(slab);
@@ -1387,9 +1389,11 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab) 


	BUG_ON(!folio_test_slab(folio));

	__slab_clear_pfmemalloc(slab);

	__folio_clear_slab(folio);

	page_mapcount_reset(folio_page(folio, 0));

	folio->mapping = NULL;

	/* Make the mapping reset visible before clearing the flag */

	smp_wmb();

	__folio_clear_slab(folio);



	if (current->reclaim_state)

		current->reclaim_state->reclaimed_slab += 1 << order;

mm/slub.c

+5 −1
Original line number Diff line number Diff line
@@ -1800,6 +1800,8 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node, 


	slab = folio_slab(folio);

	__folio_set_slab(folio);

	/* Make the flag visible before any changes to folio->mapping */

	smp_wmb();

	if (page_is_pfmemalloc(folio_page(folio, 0)))

		slab_set_pfmemalloc(slab);
@@ -2000,8 +2002,10 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab) 
	int pages = 1 << order;



	__slab_clear_pfmemalloc(slab);

	__folio_clear_slab(folio);

	folio->mapping = NULL;

	/* Make the mapping reset visible before clearing the flag */

	smp_wmb();

	__folio_clear_slab(folio);

	if (current->reclaim_state)

		current->reclaim_state->reclaimed_slab += pages;

	unaccount_slab(slab, order, s);