linux-kernel - Re: [PATCH 7/8] hugetlb: make free_huge

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Date:   Thu, 25 Mar 2021 10:32:23 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Rientjes <rientjes@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Hillf Danton <hdanton@...a.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 7/8] hugetlb: make free_huge_page irq safe

On 3/25/21 4:21 AM, Michal Hocko wrote:
> On Wed 24-03-21 17:28:34, Mike Kravetz 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, as seen in [1] this
>> does not cover all cases.  Instead, make the locks taken in the
>> free_huge_page irq safe.
> 
> I would just call out the deadlock scenario here in the changelog
> rathert than torture people by forcing them to follow up on the 0day
> report. Something like the below?
> "
> "
> 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.
>  

Thanks.  I will update changelog.

> 
>> This patch does 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@google.com/
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> 
> Acked-by: Michal Hocko <mhocko@...e.com>

And, thanks for looking at the series!
-- 
Mike Kravetz