From: Vlastimil Babka Date: Tue, 15 Dec 2020 03:04:29 +0000 (-0800) Subject: mm, slab, slub: clear the slab_cache field when freeing page X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=0c06dd75514327be4b1c22b109341ff7dfeeff98;p=linux.git mm, slab, slub: clear the slab_cache field when freeing page The page allocator expects that page->mapping is NULL for a page being freed. SLAB and SLUB use the slab_cache field which is in union with mapping, but before freeing the page, the field is referenced with the "mapping" name when set to NULL. It's IMHO more correct (albeit functionally the same) to use the slab_cache name as that's the field we use in SL*B, and document why we clear it in a comment (we don't clear fields such as s_mem or freelist, as page allocator doesn't care about those). While using the 'mapping' name would automagically keep the code correct if the unions in struct page changed, such changes should be done consciously and needed changes evaluated - the comment should help with that. Link: https://lkml.kernel.org/r/20201210160020.21562-1-vbabka@suse.cz Signed-off-by: Vlastimil Babka Acked-by: David Rientjes Acked-by: Joonsoo Kim Cc: Christoph Lameter Cc: Pekka Enberg Cc: Matthew Wilcox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/slab.c b/mm/slab.c index b1113561b98b1..2e67a513b0c9a 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -1399,7 +1399,8 @@ static void kmem_freepages(struct kmem_cache *cachep, struct page *page) __ClearPageSlabPfmemalloc(page); __ClearPageSlab(page); page_mapcount_reset(page); - page->mapping = NULL; + /* In union with page->mapping where page allocator expects NULL */ + page->slab_cache = NULL; if (current->reclaim_state) current->reclaim_state->reclaimed_slab += 1 << order; diff --git a/mm/slub.c b/mm/slub.c index 34dcc09e2ec9b..2098a544c4e24 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1836,8 +1836,8 @@ static void __free_slab(struct kmem_cache *s, struct page *page) __ClearPageSlabPfmemalloc(page); __ClearPageSlab(page); - - page->mapping = NULL; + /* In union with page->mapping where page allocator expects NULL */ + page->slab_cache = NULL; if (current->reclaim_state) current->reclaim_state->reclaimed_slab += pages; unaccount_slab_page(page, order, s);