Re: [syzbot ci] Re: Eliminate Dying Memory Cgroup

[Qi Zheng <qi.zheng@linux.dev>]

Hi Harry,

On 10/29/25 8:22 AM, Harry Yoo wrote:
> On Tue, Oct 28, 2025 at 01:58:33PM -0700, syzbot ci wrote:
>> syzbot ci has tested the following series
>>
>> [v1] Eliminate Dying Memory Cgroup
>> https://lore.kernel.org/all/cover.1761658310.git.zhengqi.arch@bytedance.com
>> * [PATCH v1 01/26] mm: memcontrol: remove dead code of checking parent memory cgroup
>> * [PATCH v1 02/26] mm: workingset: use folio_lruvec() in workingset_refault()
>> * [PATCH v1 03/26] mm: rename unlock_page_lruvec_irq and its variants
>> * [PATCH v1 04/26] mm: vmscan: refactor move_folios_to_lru()
>> * [PATCH v1 05/26] mm: memcontrol: allocate object cgroup for non-kmem case
>> * [PATCH v1 06/26] mm: memcontrol: return root object cgroup for root memory cgroup
>> * [PATCH v1 07/26] mm: memcontrol: prevent memory cgroup release in get_mem_cgroup_from_folio()
>> * [PATCH v1 08/26] buffer: prevent memory cgroup release in folio_alloc_buffers()
>> * [PATCH v1 09/26] writeback: prevent memory cgroup release in writeback module
>> * [PATCH v1 10/26] mm: memcontrol: prevent memory cgroup release in count_memcg_folio_events()
>> * [PATCH v1 11/26] mm: page_io: prevent memory cgroup release in page_io module
>> * [PATCH v1 12/26] mm: migrate: prevent memory cgroup release in folio_migrate_mapping()
>> * [PATCH v1 13/26] mm: mglru: prevent memory cgroup release in mglru
>> * [PATCH v1 14/26] mm: memcontrol: prevent memory cgroup release in mem_cgroup_swap_full()
>> * [PATCH v1 15/26] mm: workingset: prevent memory cgroup release in lru_gen_eviction()
>> * [PATCH v1 16/26] mm: thp: prevent memory cgroup release in folio_split_queue_lock{_irqsave}()
>> * [PATCH v1 17/26] mm: workingset: prevent lruvec release in workingset_refault()
>> * [PATCH v1 18/26] mm: zswap: prevent lruvec release in zswap_folio_swapin()
>> * [PATCH v1 19/26] mm: swap: prevent lruvec release in swap module
>> * [PATCH v1 20/26] mm: workingset: prevent lruvec release in workingset_activation()
>> * [PATCH v1 21/26] mm: memcontrol: prepare for reparenting LRU pages for lruvec lock
>> * [PATCH v1 22/26] mm: vmscan: prepare for reparenting traditional LRU folios
>> * [PATCH v1 23/26] mm: vmscan: prepare for reparenting MGLRU folios
>> * [PATCH v1 24/26] mm: memcontrol: refactor memcg_reparent_objcgs()
>> * [PATCH v1 25/26] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios
>> * [PATCH v1 26/26] mm: lru: add VM_WARN_ON_ONCE_FOLIO to lru maintenance helpers
>>
>> and found the following issue:
>> WARNING in folio_memcg
>>
>> Full report is available here:
>> https://ci.syzbot.org/series/0d48a77a-fb4f-485d-9fd6-086afd6fb650
>>
>> ***
>>
>> WARNING in folio_memcg
>>
>> tree:      mm-new
>> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
>> base:      b227c04932039bccc21a0a89cd6df50fa57e4716
>> arch:      amd64
>> compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
>> config:    https://ci.syzbot.org/builds/503d7034-ae99-44d1-8fb2-62e7ef5e1c7c/config
>> C repro:   https://ci.syzbot.org/findings/880c374a-1b49-436e-9be2-63d5e2c6b6ab/c_repro
>> syz repro: https://ci.syzbot.org/findings/880c374a-1b49-436e-9be2-63d5e2c6b6ab/syz_repro
>>
>> exFAT-fs (loop0): failed to load upcase table (idx : 0x00010000, chksum : 0xe5674ec2, utbl_chksum : 0xe619d30d)
>> exFAT-fs (loop0): failed to load alloc-bitmap
>> exFAT-fs (loop0): failed to recognize exfat type
>> ------------[ cut here ]------------
>> WARNING: CPU: 1 PID: 5965 at ./include/linux/memcontrol.h:380 obj_cgroup_memcg include/linux/memcontrol.h:380 [inline]
>> WARNING: CPU: 1 PID: 5965 at ./include/linux/memcontrol.h:380 folio_memcg+0x148/0x1c0 include/linux/memcontrol.h:434
> 
> This is understandable as the code snippet was added fairly recently
> and is easy to miss during rebasing.

My mistake, I should recheck it.

> 
> #syz test
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index a341814468b9..738d914e5354 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -896,11 +896,14 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>   	 * to the active LRU list in the case.
>   	 */
>   	if (comp_ret || !dlen || dlen >= PAGE_SIZE) {
> +		rcu_read_lock();
>   		if (!mem_cgroup_zswap_writeback_enabled(
>   					folio_memcg(page_folio(page)))) {
> +			rcu_read_unlock();
>   			comp_ret = comp_ret ? comp_ret : -EINVAL;
>   			goto unlock;
>   		}
> +		rcu_read_unlock();
>   		comp_ret = 0;
>   		dlen = PAGE_SIZE;
>   		dst = kmap_local_page(page);

LGTM, will do in the next version.

Thanks!

>