From: Muchun Song In the near future, a folio will no longer pin its corresponding memory cgroup. To ensure safety, it will only be appropriate to hold the rcu read lock or acquire a reference to the memory cgroup returned by folio_memcg(), thereby preventing it from being released. In the current patch, the rcu read lock is employed to safeguard against the release of the memory cgroup in mglru. This serves as a preparatory measure for the reparenting of the LRU pages. Signed-off-by: Muchun Song Signed-off-by: Qi Zheng --- mm/vmscan.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 354b19f7365d4..814498a2c1bd6 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3444,8 +3444,10 @@ static struct folio *get_pfn_folio(unsigned long pfn, struct mem_cgroup *memcg, if (folio_nid(folio) != pgdat->node_id) return NULL; + rcu_read_lock(); if (folio_memcg(folio) != memcg) - return NULL; + folio = NULL; + rcu_read_unlock(); return folio; } @@ -4202,12 +4204,12 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) unsigned long addr = pvmw->address; struct vm_area_struct *vma = pvmw->vma; struct folio *folio = pfn_folio(pvmw->pfn); - struct mem_cgroup *memcg = folio_memcg(folio); + struct mem_cgroup *memcg; struct pglist_data *pgdat = folio_pgdat(folio); - struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat); - struct lru_gen_mm_state *mm_state = get_mm_state(lruvec); - DEFINE_MAX_SEQ(lruvec); - int gen = lru_gen_from_seq(max_seq); + struct lruvec *lruvec; + struct lru_gen_mm_state *mm_state; + unsigned long max_seq; + int gen; lockdep_assert_held(pvmw->ptl); VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio); @@ -4242,6 +4244,13 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) } } + rcu_read_lock(); + memcg = folio_memcg(folio); + lruvec = mem_cgroup_lruvec(memcg, pgdat); + max_seq = READ_ONCE((lruvec)->lrugen.max_seq); + gen = lru_gen_from_seq(max_seq); + mm_state = get_mm_state(lruvec); + arch_enter_lazy_mmu_mode(); pte -= (addr - start) / PAGE_SIZE; @@ -4282,6 +4291,8 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw) if (mm_state && suitable_to_scan(i, young)) update_bloom_filter(mm_state, max_seq, pvmw->pmd); + rcu_read_unlock(); + return true; } -- 2.20.1