On 2023/7/12 2:01, Mike Kravetz wrote:
> On 07/11/23 10:05, Jiaqi Yan wrote:
>> On Mon, Jul 10, 2023 at 8:16 AM Jiaqi Yan <jiaqiyan@xxxxxxxxxx> wrote:
>>> On Fri, Jul 7, 2023 at 7:57 PM Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>>>> On 2023/7/8 4:19, Jiaqi Yan wrote:
>>>>
>>>>> + if (subpage == p->page) {
>>>>> + ret = true;
>>>>> + break;
>>>>> + }
>>>>> + }
>>>>> +
>>>>> + return ret;
>>>>> }
>>>>
>>>> It seems there's a race between __is_raw_hwp_subpage and unpoison_memory:
>>>> unpoison_memory __is_raw_hwp_subpage
>>>> if (!folio_test_hwpoison(folio)) -- hwpoison is set
>>>> folio_free_raw_hwp llist_for_each_entry_safe raw_hwp_list
>>>> llist_del_all ..
>>>> folio_test_clear_hwpoison
>>>>
>>>
>>> Thanks Miaohe for raising this concern.
>>>
>>>> But __is_raw_hwp_subpage is used in hugetlbfs, unpoison_memory couldn't reach here because there's a
>>>> folio_mapping == NULL check before folio_free_raw_hwp.
>>>
>>> I agree. But in near future I do want to make __is_raw_hwp_subpage
>>> work for shared-mapping hugetlb, so it would be nice to work with
>>> unpoison_memory. It doesn't seem to me that holding mf_mutex in
>>> __is_raw_hwp_subpage is nice or even absolutely correct. Let me think
>>> if I can come up with something in v4.
>>
>> At my 2nd thought, if __is_raw_hwp_subpage simply takes mf_mutex
>> before llist_for_each_entry, it will introduce a deadlock:
>>
>> unpoison_memory __is_raw_hwp_subpage
>> held mf_mutex held hugetlb_lock
>> get_hwpoison_hugetlb_folio attempts mf_mutex
>> attempts hugetlb lock
>>
>> Not for this patch series, but for future, is it a good idea to make
>> mf_mutex available to hugetlb code? Then enforce the order of locking
>> to be mf_mutex first, hugetlb_lock second? I believe this is the
>> current locking pattern / order for try_memory_failure_hugetlb.
>
> I think only holding mf_mutex in __is_raw_hwp_subpage would be sufficient
> to prevent races with unpoison_memory. memory failure code needs to take
Since soft_offline_page, memory_failure and unpoison_memory both holds mf_mutex,
I think this should be enough to prevent races between them too.
Thanks.
