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

From: Mike Kravetz
Date: Thu Dec 12 2019 - 14:23:13 EST

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.

Do you have a test to reproduce the issue? If so, can you try running with
this patch.
Mike Kravetz