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

From: Mike Kravetz <mike.kravetz@oracle.com>
To: Michal Hocko <mhocko@suse.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
	Oscar Salvador <osalvador@suse.de>,
	David Hildenbrand <david@redhat.com>,
	Muchun Song <songmuchun@bytedance.com>,
	David Rientjes <rientjes@google.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Matthew Wilcox <willy@infradead.org>,
	HORIGUCHI NAOYA <naoya.horiguchi@nec.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
	Waiman Long <longman@redhat.com>, Peter Xu <peterx@redhat.com>,
	Mina Almasry <almasrymina@google.com>,
	Hillf Danton <hdanton@sina.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 7/8] hugetlb: make free_huge_page irq safe
Date: Thu, 25 Mar 2021 10:32:23 -0700	[thread overview]
Message-ID: <3a468388-8845-d3ba-67fe-67138781055e@oracle.com> (raw)
In-Reply-To: <YFxyJKR+hHEMwH2i@dhcp22.suse.cz>

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@oracle.com>
> 
> Acked-by: Michal Hocko <mhocko@suse.com>

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