From b0dc3a342af36f95a68fe229b8f0f73552c5ca08 Mon Sep 17 00:00:00 2001 From: Gu Zheng Date: Wed, 25 Mar 2015 15:55:20 -0700 Subject: [PATCH] mm/memory hotplug: postpone the reset of obsolete pgdat Qiu Xishi reported the following BUG when testing hot-add/hot-remove node under stress condition: BUG: unable to handle kernel paging request at 0000000000025f60 IP: next_online_pgdat+0x1/0x50 PGD 0 Oops: 0000 [#1] SMP ACPI: Device does not support D3cold 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] CPU: 23 PID: 238 Comm: kworker/23:1 Tainted: G O 3.10.15-5885-euler0302 #1 Hardware name: HUAWEI TECHNOLOGIES CO.,LTD. Huawei N1/Huawei N1, BIOS V100R001 03/02/2015 Workqueue: events vmstat_update task: ffffa800d32c0000 ti: ffffa800d32ae000 task.ti: ffffa800d32ae000 RIP: 0010: next_online_pgdat+0x1/0x50 RSP: 0018:ffffa800d32afce8 EFLAGS: 00010286 RAX: 0000000000001440 RBX: ffffffff81da53b8 RCX: 0000000000000082 RDX: 0000000000000000 RSI: 0000000000000082 RDI: 0000000000000000 RBP: ffffa800d32afd28 R08: ffffffff81c93bfc R09: ffffffff81cbdc96 R10: 00000000000040ec R11: 00000000000000a0 R12: ffffa800fffb3440 R13: ffffa800d32afd38 R14: 0000000000000017 R15: ffffa800e6616800 FS: 0000000000000000(0000) GS:ffffa800e6600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000025f60 CR3: 0000000001a0b000 CR4: 00000000001407e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: refresh_cpu_vm_stats+0xd0/0x140 vmstat_update+0x11/0x50 process_one_work+0x194/0x3d0 worker_thread+0x12b/0x410 kthread+0xc6/0xd0 ret_from_fork+0x7c/0xb0 The cause is the "memset(pgdat, 0, sizeof(*pgdat))" at the end of try_offline_node, which will reset all the content of pgdat to 0, as the pgdat is accessed lock-free, so that the users still using the pgdat will panic, such as the vmstat_update routine. process A: offline node XX: vmstat_updat() refresh_cpu_vm_stats() 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)) zone = next_zone(zone) pg_data_t *pgdat = zone->zone_pgdat; // here pgdat is NULL now next_online_pgdat(pgdat) next_online_node(pgdat->node_id); // NULL pointer access So the solution here is postponing the reset of obsolete pgdat from try_offline_node() to hotadd_new_pgdat(), and just resetting pgdat->nr_zones and pgdat->classzone_idx to be 0 rather than the memset 0 to avoid breaking pointer information in pgdat. Signed-off-by: Gu Zheng Reported-by: Xishi Qiu Suggested-by: KAMEZAWA Hiroyuki Cc: David Rientjes Cc: Yasuaki Ishimatsu Cc: Taku Izumi Cc: Tang Chen Cc: Xie XiuQi Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory_hotplug.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 9fab10795bea..65842d688b7c 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1092,6 +1092,10 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start) return NULL; arch_refresh_nodedata(nid, pgdat); + } else { + /* Reset the nr_zones and classzone_idx to 0 before reuse */ + pgdat->nr_zones = 0; + pgdat->classzone_idx = 0; } /* we can use NODE_DATA(nid) from here */ @@ -1977,15 +1981,6 @@ void try_offline_node(int nid) if (is_vmalloc_addr(zone->wait_table)) vfree(zone->wait_table); } - - /* - * Since there is no way to guarentee the address of pgdat/zone is not - * on stack of any kernel threads or used by other kernel objects - * without reference counting or other symchronizing method, do not - * reset node_data and free pgdat here. Just reset it to 0 and reuse - * the memory when the node is online again. - */ - memset(pgdat, 0, sizeof(*pgdat)); } EXPORT_SYMBOL(try_offline_node); -- 2.20.1