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Wed, 18 Dec 2019 01:02:03 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xBI0wvuw167129; Wed, 18 Dec 2019 01:02:02 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 2wxm5kx7n5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 18 Dec 2019 01:02:02 +0000 Received: from abhmp0019.oracle.com (abhmp0019.oracle.com [141.146.116.25]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xBI11xjJ007072; Wed, 18 Dec 2019 01:01:59 GMT Received: from [192.168.1.206] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 17 Dec 2019 17:01:59 -0800 Subject: Re: [PATCH v3] mm/hugetlb: Defer freeing of huge pages if in non-task context To: Waiman Long , Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Davidlohr Bueso , Andi Kleen , Michal Hocko , "Aneesh Kumar K.V" , Kirill Tkhai References: <20191217170331.30893-1-longman@redhat.com> From: Mike Kravetz Message-ID: <8e4b9a22-a0ca-1659-9f5b-6e1acff5a57b@oracle.com> Date: Tue, 17 Dec 2019 17:01:58 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20191217170331.30893-1-longman@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9474 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-1912180005 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9474 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-1912180005 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 12/17/19 9:03 AM, Waiman Long wrote: > The following lockdep splat was observed when a certain hugetlbfs test > was run: > > [ 612.388273] ================================ > [ 612.411273] WARNING: inconsistent lock state > [ 612.432273] 4.18.0-159.el8.x86_64+debug #1 Tainted: G W --------- - - > [ 612.469273] -------------------------------- > [ 612.489273] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. > [ 612.517273] swapper/30/0 [HC0[0]:SC1[1]:HE1:SE0] takes: > [ 612.541273] ffffffff9acdc038 (hugetlb_lock){+.?.}, at: free_huge_page+0x36f/0xaa0 > [ 612.576273] {SOFTIRQ-ON-W} state was registered at: > [ 612.598273] lock_acquire+0x14f/0x3b0 > [ 612.616273] _raw_spin_lock+0x30/0x70 > [ 612.634273] __nr_hugepages_store_common+0x11b/0xb30 > [ 612.657273] hugetlb_sysctl_handler_common+0x209/0x2d0 > [ 612.681273] proc_sys_call_handler+0x37f/0x450 > [ 612.703273] vfs_write+0x157/0x460 > [ 612.719273] ksys_write+0xb8/0x170 > [ 612.736273] do_syscall_64+0xa5/0x4d0 > [ 612.753273] entry_SYSCALL_64_after_hwframe+0x6a/0xdf > [ 612.777273] irq event stamp: 691296 > [ 612.794273] hardirqs last enabled at (691296): [] _raw_spin_unlock_irqrestore+0x4b/0x60 > [ 612.839273] hardirqs last disabled at (691295): [] _raw_spin_lock_irqsave+0x22/0x81 > [ 612.882273] softirqs last enabled at (691284): [] irq_enter+0xc3/0xe0 > [ 612.922273] softirqs last disabled at (691285): [] irq_exit+0x23e/0x2b0 > [ 612.962273] > [ 612.962273] other info that might help us debug this: > [ 612.993273] Possible unsafe locking scenario: > [ 612.993273] > [ 613.020273] CPU0 > [ 613.031273] ---- > [ 613.042273] lock(hugetlb_lock); > [ 613.057273] > [ 613.069273] lock(hugetlb_lock); > [ 613.085273] > [ 613.085273] *** DEADLOCK *** > : > [ 613.245273] Call Trace: > [ 613.256273] > [ 613.265273] dump_stack+0x9a/0xf0 > [ 613.281273] mark_lock+0xd0c/0x12f0 > [ 613.297273] ? print_shortest_lock_dependencies+0x80/0x80 > [ 613.322273] ? sched_clock_cpu+0x18/0x1e0 > [ 613.341273] __lock_acquire+0x146b/0x48c0 > [ 613.360273] ? trace_hardirqs_on+0x10/0x10 > [ 613.379273] ? trace_hardirqs_on_caller+0x27b/0x580 > [ 613.401273] lock_acquire+0x14f/0x3b0 > [ 613.419273] ? free_huge_page+0x36f/0xaa0 > [ 613.440273] _raw_spin_lock+0x30/0x70 > [ 613.458273] ? free_huge_page+0x36f/0xaa0 > [ 613.477273] free_huge_page+0x36f/0xaa0 > [ 613.495273] bio_check_pages_dirty+0x2fc/0x5c0 > [ 613.516273] clone_endio+0x17f/0x670 [dm_mod] > [ 613.536273] ? disable_discard+0x90/0x90 [dm_mod] > [ 613.558273] ? bio_endio+0x4ba/0x930 > [ 613.575273] ? blk_account_io_completion+0x400/0x530 > [ 613.598273] blk_update_request+0x276/0xe50 > [ 613.617273] scsi_end_request+0x7b/0x6a0 > [ 613.636273] ? lock_downgrade+0x6f0/0x6f0 > [ 613.654273] scsi_io_completion+0x1c6/0x1570 > [ 613.674273] ? sd_completed_bytes+0x3a0/0x3a0 [sd_mod] > [ 613.698273] ? scsi_mq_requeue_cmd+0xc0/0xc0 > [ 613.718273] blk_done_softirq+0x22e/0x350 > [ 613.737273] ? blk_softirq_cpu_dead+0x230/0x230 > [ 613.758273] __do_softirq+0x23d/0xad8 > [ 613.776273] irq_exit+0x23e/0x2b0 > [ 613.792273] do_IRQ+0x11a/0x200 > [ 613.806273] common_interrupt+0xf/0xf > [ 613.823273] > > Both the hugetbl_lock and the subpool lock can be acquired in > free_huge_page(). One way to solve the problem is to make both locks > irq-safe. However, Mike Kravetz had learned that the hugetlb_lock is > held for a linear scan of ALL hugetlb pages during a cgroup reparentling > operation. So it is just too long to have irq disabled unless we can > break hugetbl_lock down into finer-grained locks with shorter lock > hold times. > > Another alternative is to defer the freeing to a workqueue job. This > patch implements the deferred freeing by adding a free_hpage_workfn() > work function to do the actual freeing. The free_huge_page() call in > a non-task context saves the page to be freed in the hpage_freelist > linked list in a lockless manner using the llist APIs. > > The generic workqueue is used to process the work, but a dedicated > workqueue can be used instead if it is desirable to have the huge page > freed ASAP. > ----> > Thanks to Kirill Tkhai for suggesting the use > of llist APIs which simplfy the code. > > [v2: Add more comment & remove unneeded racing check] > [v3: Update commit log, remove pr_debug & use llist APIs] <---- IMO, Those lines should not be in the commit message. > Reported-by: Aneesh Kumar K.V I would just drop this 'Reported-by: Aneesh ...'. Yes, Aneesh did report a problem that was triggered by the same underlying issue. But the splat he reported was very different. > Signed-off-by: Waiman Long Thanks for doing this, Reviewed-by: Mike Kravetz -- Mike Kravetz