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

From: Waiman Long
Date: Thu Dec 12 2019 - 15:52:31 EST

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]
>> [2]
>> 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.