Re: [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue

[Waiman Long]

On 12/12/19 2:22 PM, Mike Kravetz wrote:
> On 12/12/19 11:04 AM, Davidlohr Bueso wrote:
>> There have been deadlock reports[1, 2] where put_page is called
>> from softirq context and this causes trouble with the hugetlb_lock,
>> as well as potentially the subpool lock.
>>
>> For such an unlikely scenario, lets not add irq dancing overhead
>> to the lock+unlock operations, which could incur in expensive
>> instruction dependencies, particularly when considering hard-irq
>> safety. For example PUSHF+POPF on x86.
>>
>> Instead, just use a workqueue and do the free_huge_page() in regular
>> task context.
>>
>> [1] https://lore.kernel.org/lkml/20191211194615.18502-1-longman@xxxxxxxxxx/
>> [2] https://lore.kernel.org/lkml/20180905112341.21355-1-aneesh.kumar@xxxxxxxxxxxxx/
>>
>> Reported-by: Waiman Long <longman@xxxxxxxxxx>
>> Reported-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
>> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
> Thank you Davidlohr.
>
> The patch does seem fairly simple and straight forward.  I need to brush up
> on my workqueue knowledge to provide a full review.
>
> Longman,
> Do you have a test to reproduce the issue?  If so, can you try running with
> this patch.

Yes, I do have a test that can reproduce the issue. I will run it with
the patch and report the status tomorrow.

-Longman