mm, madvise: fix potential workingset node list_lru leaks

Since commit 5abc1e37afa0 ("mm: list_lru: allocate list_lru_one only when
needed"), all list_lru users need to allocate the items using the new
infrastructure that provides list_lru info for slab allocation, ensuring
that the corresponding memcg list_lru is allocated before use.

For workingset shadow nodes (which are xa_node), users are converted to
use the new infrastructure by commit 9bbdc0f32409 ("xarray: use
kmem_cache_alloc_lru to allocate xa_node").  The xas->xa_lru will be set
correctly for filemap users.  However, there is a missing case: xa_node
allocations caused by madvise(..., MADV_COLLAPSE).

madvise(..., MADV_COLLAPSE) will also read in the absent parts of file
map, and there will be xa_nodes allocated for the caller's memcg (assuming
it's not rootcg).  However, these allocations won't trigger memcg list_lru
allocation because the proper xas info was not set.

If nothing else has allocated other xa_nodes for that memcg to trigger
list_lru creation, and memory pressure starts to evict file pages,
workingset_update_node will try to add these xa_nodes to their
corresponding memcg list_lru, and it does not exist (NULL).  So they will
be added to rootcg's list_lru instead.

This shouldn't be a significant issue in practice, but it is indeed
unexpected behavior, and these xa_nodes will not be reclaimed effectively.
And may lead to incorrect counting of the list_lru->nr_items counter.

This problem wasn't exposed until recent commit 28e98022b31ef
("mm/list_lru: simplify reparenting and initial allocation") added a
sanity check: only dying memcg could have a NULL list_lru when
list_lru_{add,del} is called.  This problem triggered this WARNING.

So make madvise(..., MADV_COLLAPSE) also call xas_set_lru() to pass the
list_lru which we may want to insert xa_node into later.  And move
mapping_set_update to mm/internal.h, and turn into a macro to avoid
including extra headers in mm/internal.h.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 9bbdc0f32409 ("xarray: use kmem_cache_alloc_lru to allocate xa_node")
Reported-by: [email protected]
Closes: https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Kairui Song <[email protected]>
Cc: Chengming Zhou <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Qi Zheng <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Yu Zhao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 0 insertions, 9 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index f61cf51c2238..33b60d448fca 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -124,15 +124,6 @@
  *    ->private_lock		(zap_pte_range->block_dirty_folio)
  */
 
-static void mapping_set_update(struct xa_state *xas,
-		struct address_space *mapping)
-{
-	if (dax_mapping(mapping) || shmem_mapping(mapping))
-		return;
-	xas_set_update(xas, workingset_update_node);
-	xas_set_lru(xas, &shadow_nodes);
-}
-
 static void page_cache_delete(struct address_space *mapping,
 				   struct folio *folio, void *shadow)
 {