Re: [PATCH] mm: memcg: fix split queue list crash when large folio migration

[Nhat Pham <nphamcs@gmail.com>]

On Tue, Dec 19, 2023 at 10:52 PM Baolin Wang
<baolin.wang@linux.alibaba.com> wrote:
>
> When running autonuma with enabling multi-size THP, I encountered the following
> kernel crash issue:
>
> [  134.290216] list_del corruption. prev->next should be fffff9ad42e1c490,
> but was dead000000000100. (prev=fffff9ad42399890)
> [  134.290877] kernel BUG at lib/list_debug.c:62!
> [  134.291052] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> [  134.291210] CPU: 56 PID: 8037 Comm: numa01 Kdump: loaded Tainted:
> G            E      6.7.0-rc4+ #20
> [  134.291649] RIP: 0010:__list_del_entry_valid_or_report+0x97/0xb0
> ......
> [  134.294252] Call Trace:
> [  134.294362]  <TASK>
> [  134.294440]  ? die+0x33/0x90
> [  134.294561]  ? do_trap+0xe0/0x110
> ......
> [  134.295681]  ? __list_del_entry_valid_or_report+0x97/0xb0
> [  134.295842]  folio_undo_large_rmappable+0x99/0x100
> [  134.296003]  destroy_large_folio+0x68/0x70
> [  134.296172]  migrate_folio_move+0x12e/0x260
> [  134.296264]  ? __pfx_remove_migration_pte+0x10/0x10
> [  134.296389]  migrate_pages_batch+0x495/0x6b0
> [  134.296523]  migrate_pages+0x1d0/0x500
> [  134.296646]  ? __pfx_alloc_misplaced_dst_folio+0x10/0x10
> [  134.296799]  migrate_misplaced_folio+0x12d/0x2b0
> [  134.296953]  do_numa_page+0x1f4/0x570
> [  134.297121]  __handle_mm_fault+0x2b0/0x6c0
> [  134.297254]  handle_mm_fault+0x107/0x270
> [  134.300897]  do_user_addr_fault+0x167/0x680
> [  134.304561]  exc_page_fault+0x65/0x140
> [  134.307919]  asm_exc_page_fault+0x22/0x30
>
> The reason for the crash is that, the commit 85ce2c517ade ("memcontrol: only
> transfer the memcg data for migration") removed the charging and uncharging
> operations of the migration folios and cleared the memcg data of the old folio.
>
> During the subsequent release process of the old large folio in destroy_large_folio(),
> if the large folio needs to be removed from the split queue, an incorrect split
> queue can be obtained (which is pgdat->deferred_split_queue) because the old
> folio's memcg is NULL now. This can lead to list operations being performed
> under the wrong split queue lock protection, resulting in a list crash as above.

Ah this is tricky. I think you're right - the old folio's memcg is
used to get the deferred split queue, and we cleared it here :)

>
> After the migration, the old folio is going to be freed, so we can remove it
> from the split queue in mem_cgroup_migrate() a bit earlier before clearing the
> memcg data to avoid getting incorrect split queue.
>
> Fixes: 85ce2c517ade ("memcontrol: only transfer the memcg data for migration")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>  mm/huge_memory.c |  2 +-
>  mm/memcontrol.c  | 11 +++++++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 6be1a380a298..c50dc2e1483f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3124,7 +3124,7 @@ void folio_undo_large_rmappable(struct folio *folio)
>         spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>         if (!list_empty(&folio->_deferred_list)) {
>                 ds_queue->split_queue_len--;
> -               list_del(&folio->_deferred_list);
> +               list_del_init(&folio->_deferred_list);
>         }
>         spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>  }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ae8c62c7aa53..e66e0811cccc 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7575,6 +7575,17 @@ void mem_cgroup_migrate(struct folio *old, struct folio *new)
>
>         /* Transfer the charge and the css ref */
>         commit_charge(new, memcg);
> +       /*
> +        * If the old folio a large folio and is in the split queue, it needs
> +        * to be removed from the split queue now, in case getting an incorrect
> +        * split queue in destroy_large_folio() after the memcg of the old folio
> +        * is cleared.
> +        *
> +        * In addition, the old folio is about to be freed after migration, so
> +        * removing from the split queue a bit earlier seems reasonable.
> +        */
> +       if (folio_test_large(old) && folio_test_large_rmappable(old))
> +               folio_undo_large_rmappable(old);

This looks reasonable to me :)
Reviewed-by: Nhat Pham <nphamcs@gmail.com>

>         old->memcg_data = 0;
>  }
>
> --
> 2.39.3
>