Re: [External] [PATCH v3 7/8] hugetlb: make free_huge_page irq safe

[Mike Kravetz]

On 4/2/21 5:47 AM, Muchun Song wrote:
> On Wed, Mar 31, 2021 at 11:42 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>>
>> Commit c77c0a8ac4c5 ("mm/hugetlb: defer freeing of huge pages if in
>> non-task context") was added to address the issue of free_huge_page
>> being called from irq context.  That commit hands off free_huge_page
>> processing to a workqueue if !in_task.  However, this doesn't cover
>> all the cases as pointed out by 0day bot lockdep report [1].
>>
>> :  Possible interrupt unsafe locking scenario:
>> :
>> :        CPU0                    CPU1
>> :        ----                    ----
>> :   lock(hugetlb_lock);
>> :                                local_irq_disable();
>> :                                lock(slock-AF_INET);
>> :                                lock(hugetlb_lock);
>> :   <Interrupt>
>> :     lock(slock-AF_INET);
>>
>> Shakeel has later explained that this is very likely TCP TX zerocopy
>> from hugetlb pages scenario when the networking code drops a last
>> reference to hugetlb page while having IRQ disabled. Hugetlb freeing
>> path doesn't disable IRQ while holding hugetlb_lock so a lock dependency
>> chain can lead to a deadlock.
>>
>> This commit addresses the issue by doing the following:
>> - Make hugetlb_lock irq safe.  This is mostly a simple process of
>>   changing spin_*lock calls to spin_*lock_irq* calls.
>> - Make subpool lock irq safe in a similar manner.
>> - Revert the !in_task check and workqueue handoff.
>>
>> [1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43aadc@xxxxxxxxxx/
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> 
> Hi Mike,
> 
> Today I pulled the newest code (next-20210401). I found that
> alloc_and_dissolve_huge_page is not updated. In this function,
> hugetlb_lock is still non-irq safe. Maybe you or Oscar need
> to fix.
> 
> Thanks.

Thank you Muchun,

Oscar's changes were not in Andrew's tree when I started on this series
and I failed to notice their inclusion.  In addition,
isolate_or_dissolve_huge_page also needs updating as well as a change in
set_max_huge_pages that was omitted while rebasing.

Andrew, the following patch addresses those missing changes.  Ideally,
the changes should be combined/included in this patch.  If you want me
to sent another version of this patch or another series, let me know.