From 8b8817630ae80032e80b2eaf334de756ac1ff6a3 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 4 Nov 2022 15:57:26 +0100 Subject: 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: kernel test robot Signed-off-by: Vlastimil Babka Acked-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> --- mm/slab.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'mm/slab.c') diff --git a/mm/slab.c b/mm/slab.c index 59c8e28f7b6a..219beb48588e 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -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; -- cgit