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Thu, 25 Mar 2021 17:32:26 +0000 Subject: Re: [PATCH 7/8] hugetlb: make free_huge_page irq safe To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Roman Gushchin , Shakeel Butt , Oscar Salvador , David Hildenbrand , Muchun Song , David Rientjes , Miaohe Lin , Peter Zijlstra , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Hillf Danton , Andrew Morton References: <20210325002835.216118-1-mike.kravetz@oracle.com> <20210325002835.216118-8-mike.kravetz@oracle.com> From: Mike Kravetz Message-ID: <3a468388-8845-d3ba-67fe-67138781055e@oracle.com> Date: Thu, 25 Mar 2021 10:32:23 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: CO2PR18CA0052.namprd18.prod.outlook.com (2603:10b6:104:2::20) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by CO2PR18CA0052.namprd18.prod.outlook.com (2603:10b6:104:2::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.25 via Frontend Transport; Thu, 25 Mar 2021 17:32:25 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 3f815f31-6f0a-4d54-321f-08d8efb3f50c X-MS-TrafficTypeDiagnostic: SJ0PR10MB4413: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; 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identity=mailfrom; envelope-from=""; helo=aserp2120.oracle.com; client-ip=141.146.126.78 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616693569-593681 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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); > : > : 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 > > Acked-by: Michal Hocko And, thanks for looking at the series! -- Mike Kravetz