From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f178.google.com (mail-ob0-f178.google.com [209.85.214.178]) by kanga.kvack.org (Postfix) with ESMTP id 4B50F6B0038 for ; Wed, 4 Mar 2015 03:32:21 -0500 (EST) Received: by obcuz6 with SMTP id uz6so5365329obc.9 for ; Wed, 04 Mar 2015 00:32:21 -0800 (PST) Received: from szxga02-in.huawei.com (szxga02-in.huawei.com. [119.145.14.65]) by mx.google.com with ESMTPS id e7si1748441obf.19.2015.03.04.00.32.13 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 04 Mar 2015 00:32:20 -0800 (PST) Message-ID: <54F6C2E6.4030500@huawei.com> Date: Wed, 4 Mar 2015 16:31:34 +0800 From: Xie XiuQi MIME-Version: 1.0 Subject: Re: node-hotplug: is memset 0 safe in try_offline_node()? References: <54F52ACF.4030103@huawei.com> <54F58AE3.50101@cn.fujitsu.com> <54F66C52.4070600@huawei.com> <54F681A7.4050203@cn.fujitsu.com> In-Reply-To: <54F681A7.4050203@cn.fujitsu.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Gu Zheng , Xishi Qiu Cc: Yasuaki Ishimatsu , Andrew Morton , Tang Chen , Yinghai Lu , Linux MM , LKML , Toshi Kani , Mel Gorman , Tejun Heo , Hanjun Guo On 2015/3/4 11:53, Gu Zheng wrote: > Hi Xishi, > > On 03/04/2015 10:22 AM, Xishi Qiu wrote: > >> On 2015/3/3 18:20, Gu Zheng wrote: >> >>> Hi Xishi, >>> On 03/03/2015 11:30 AM, Xishi Qiu wrote: >>> >>>> When hot-remove a numa node, we will clear pgdat, >>>> but is memset 0 safe in try_offline_node()? >>> >>> It is not safe here. In fact, this is a temporary solution here. >>> As you know, pgdat is accessed lock-less now, so protection >>> mechanism (RCUi 1/4 ?) is needed to make it completely safe here, >>> but it seems a bit over-kill. >>> >>>> >>>> process A: offline node XX: >>>> for_each_populated_zone() >>>> find online node XX >>>> cond_resched() >>>> offline cpu and memory, then try_offline_node() >>>> node_set_offline(nid), and memset(pgdat, 0, sizeof(*pgdat)) >>>> access node XX's pgdat >>>> NULL pointer access error >>> >>> It's possible, but I did not meet this condition, did you? >>> >> >> Yes, we test hot-add/hot-remove node with stress, and meet the following >> call trace several times. > > Thanks. > >> >> next_online_pgdat() >> int nid = next_online_node(pgdat->node_id); // it's here, pgdat is NULL > > memset(pgdat, 0, sizeof(*pgdat)); > This memset just sets the context of pgdat to 0, but it will not free pgdat, so the *pgdat is > NULL* is strange here. Hi Gu, This pgdat isn't 0, but pgdat->zone[i]->zone_pgdat is 0. So pgdat is 0 in next_zone(). -- /* * next_zone - helper magic for for_each_zone() */ struct zone *next_zone(struct zone *zone) { pg_data_t *pgdat = zone->zone_pgdat; if (zone < pgdat->node_zones + MAX_NR_ZONES - 1) zone++; else { pgdat = next_online_pgdat(pgdat); if (pgdat) zone = pgdat->node_zones; else zone = NULL; } return zone; } > But anyway, the bug is real, we must fix it. > > Regards, > Gu > >> >> I add some printk, it shows the above pgdat is just the offline node's pgdat. >> The reason may be that for_each_zone() and for_each_populated_zone() are lock-less. >> And stop machine could not resolve it, because cond_resched() maybe in cyclical code. >> >> [ 1422.011064] BUG: unable to handle kernel paging request at 0000000000025f60 >> [ 1422.011086] IP: [] next_online_pgdat+0x1/0x50 >> [ 1422.011178] PGD 0 >> [ 1422.011180] Oops: 0000 [#1] SMP >> [ 1422.011409] ACPI: Device does not support D3cold >> [ 1422.011961] Modules linked in: fuse nls_iso8859_1 nls_cp437 vfat fat loop dm_mod coretemp mperf crc32c_intel ghash_clmulni_intel aesni_intel ablk_helper cryptd lrw gf128mul glue_helper aes_x86_64 pcspkr microcode igb dca i2c_algo_bit ipv6 megaraid_sas iTCO_wdt i2c_i801 i2c_core iTCO_vendor_support tg3 sg hwmon ptp lpc_ich pps_core mfd_core acpi_pad rtc_cmos button ext3 jbd mbcache sd_mod crc_t10dif scsi_dh_alua scsi_dh_rdac scsi_dh_hp_sw scsi_dh_emc scsi_dh ahci libahci libata scsi_mod [last unloaded: rasf] >> [ 1422.012006] CPU: 23 PID: 238 Comm: kworker/23:1 Tainted: G O 3.10.15-5885-euler0302 #1 >> [ 1422.012024] Hardware name: HUAWEI TECHNOLOGIES CO.,LTD. Huawei N1/Huawei N1, BIOS V100R001 03/02/2015 >> [ 1422.012065] Workqueue: events vmstat_update >> [ 1422.012084] task: ffffa800d32c0000 ti: ffffa800d32ae000 task.ti: ffffa800d32ae000 >> [ 1422.012165] RIP: 0010:[] [] next_online_pgdat+0x1/0x50 >> [ 1422.012205] RSP: 0018:ffffa800d32afce8 EFLAGS: 00010286 >> [ 1422.012225] RAX: 0000000000001440 RBX: ffffffff81da53b8 RCX: 0000000000000082 >> [ 1422.012226] RDX: 0000000000000000 RSI: 0000000000000082 RDI: 0000000000000000 >> [ 1422.012254] RBP: ffffa800d32afd28 R08: ffffffff81c93bfc R09: ffffffff81cbdc96 >> [ 1422.012272] R10: 00000000000040ec R11: 00000000000000a0 R12: ffffa800fffb3440 >> [ 1422.012290] R13: ffffa800d32afd38 R14: 0000000000000017 R15: ffffa800e6616800 >> [ 1422.012292] FS: 0000000000000000(0000) GS:ffffa800e6600000(0000) knlGS:0000000000000000 >> [ 1422.012314] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 1422.012328] CR2: 0000000000025f60 CR3: 0000000001a0b000 CR4: 00000000001407e0 >> [ 1422.012328] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> [ 1422.012328] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> [ 1422.012328] Stack: >> [ 1422.012328] ffffa800d32afd28 ffffffff81126ca5 ffffa800ffffffff ffffffff814b4314 >> [ 1422.012328] ffffa800d32ae010 0000000000000000 ffffa800e6616180 ffffa800fffb3440 >> [ 1422.012328] ffffa800d32afde8 ffffffff81128220 ffffffff00000013 0000000000000038 >> [ 1422.012328] Call Trace: >> [ 1422.012328] [] ? next_zone+0xc5/0x150 >> [ 1422.012328] [] ? __schedule+0x544/0x780 >> [ 1422.012328] [] refresh_cpu_vm_stats+0xd0/0x140 >> [ 1422.012328] [] vmstat_update+0x11/0x50 >> [ 1422.012328] [] process_one_work+0x194/0x3d0 >> [ 1422.012328] [] worker_thread+0x12b/0x410 >> [ 1422.012328] [] ? manage_workers+0x1a0/0x1a0 >> [ 1422.012328] [] kthread+0xc6/0xd0 >> [ 1422.012328] [] ? kthread_freezable_should_stop+0x70/0x70 >> [ 1422.012328] [] ret_from_fork+0x7c/0xb0 >> [ 1422.012328] [] ? kthread_freezable_should_stop+0x70/0x70 >> >> Thanks, >> Xishi Qiu >> >>> Regards, >>> Gu >>> >>>> >>>> Thanks, >>>> Xishi Qiu >>>> >>>> -- >>>> To unsubscribe, send a message with 'unsubscribe linux-mm' in >>>> the body to majordomo@kvack.org. For more info on Linux MM, >>>> see: http://www.linux-mm.org/ . >>>> Don't email: email@kvack.org >>>> >>> >>> >>> >>> . >>> >> >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> . >> > > > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org