From: Qi Zheng The mglru page table walker batches per-generation size deltas in walk->nr_pages while walking page tables without holding the lruvec lock. The reset_batch_size() later folds those deltas into walk->lruvec under the lruvec lock. The page table walker can run concurrently with the memcg reparenting path as follows: CPU0 CPU1 ==== ==== walk_mm --> walk_page_range --> update_batch_size --> walk->nr_pages += delta mem_cgroup_css_offline --> memcg_reparent_objcgs --> lock lruvec lru_gen_reparent_memcg --> reparent child folios to parent unlock lruvec lock lruvec reset_batch_size --> child lrugen->nr_pages += delta This can trigger the following warning: WARNING: mm/vmscan.c:5867 at lru_gen_exit_memcg+0x26f/0x300 RIP: 0010:lru_gen_exit_memcg+0x26f/0x300 mm/vmscan.c:5867 Call Trace: mem_cgroup_free mm/memcontrol.c:3972 [inline] mem_cgroup_css_free+0x76/0xb0 mm/memcontrol.c:4241 css_free_rwork_fn+0x125/0x1260 kernel/cgroup/cgroup.c:5575 process_one_work+0xa0d/0x1c30 kernel/workqueue.c:3314 process_scheduled_works kernel/workqueue.c:3397 [inline] worker_thread+0x645/0xe80 kernel/workqueue.c:3478 kthread+0x367/0x480 kernel/kthread.c:436 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 To fix it, add lrugen->reparented to remember the new owner of a reparented lruvec, and make reset_batch_size() charge pending deltas to that owner. Reported-by: Peiyang He Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios") Cc: Signed-off-by: Qi Zheng --- include/linux/mmzone.h | 4 ++++ mm/vmscan.c | 43 +++++++++++++++++++++++++++++++++++------- 2 files changed, 40 insertions(+), 7 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index ca2712187147..0d572db2ef64 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -584,6 +584,10 @@ struct lru_gen_folio { u8 gen; /* the list segment this lru_gen_folio belongs to */ u8 seg; +#ifdef CONFIG_MEMCG + /* the lruvec this lruvec has been reparented to */ + struct lruvec *reparented; +#endif /* per-node lru_gen_folio list for global reclaim */ struct hlist_nulls_node list; }; diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96..64362cbed814 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3262,10 +3262,37 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio, walk->nr_pages[new_gen][type][zone] += delta; } +#ifdef CONFIG_MEMCG +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) +{ + struct lruvec *reparented; + + for (;;) { + lruvec_lock_irq(lruvec); + + reparented = lruvec->lrugen.reparented; + if (!reparented) + break; + + lruvec_unlock_irq(lruvec); + lruvec = reparented; + } + + return lruvec; +} +#else +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) +{ + lruvec_lock_irq(lruvec); + + return lruvec; +} +#endif + static void reset_batch_size(struct lru_gen_mm_walk *walk) { int gen, type, zone; - struct lruvec *lruvec = walk->lruvec; + struct lruvec *lruvec = lock_batch_lruvec(walk->lruvec); struct lru_gen_folio *lrugen = &lruvec->lrugen; walk->batched = 0; @@ -3285,6 +3312,8 @@ static void reset_batch_size(struct lru_gen_mm_walk *walk) lru += LRU_ACTIVE; __update_lru_size(lruvec, lru, zone, delta); } + + lruvec_unlock_irq(lruvec); } static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *args) @@ -3779,11 +3808,8 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk) mmap_read_unlock(mm); } - if (walk->batched) { - lruvec_lock_irq(lruvec); + if (walk->batched) reset_batch_size(walk); - lruvec_unlock_irq(lruvec); - } cond_resched(); } while (err == -EAGAIN); @@ -4563,6 +4589,8 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent, mem_cgroup_update_lru_size(parent_lruvec, lru, zid, size); } } + + child_lruvec->lrugen.reparented = parent_lruvec; } #endif /* CONFIG_MEMCG */ @@ -4867,9 +4895,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, walk = current->reclaim_state->mm_walk; if (walk && walk->batched) { walk->lruvec = lruvec; - lruvec_lock_irq(lruvec); reset_batch_size(walk); - lruvec_unlock_irq(lruvec); } mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc), @@ -5784,6 +5810,9 @@ void lru_gen_init_lruvec(struct lruvec *lruvec) lrugen->max_seq = MIN_NR_GENS + 1; lrugen->enabled = lru_gen_enabled(); +#ifdef CONFIG_MEMCG + lrugen->reparented = NULL; +#endif for (i = 0; i <= MIN_NR_GENS + 1; i++) lrugen->timestamps[i] = jiffies; -- 2.54.0