It is a bit frustrating, but if there's a workaround with disabling delegations that would at least be welcome news. We have a Kerberized environment and ACLs are a huge selling point for v4. To the latter point, I get the impression that either there aren't too many organizations using NFS at the scale that both yours and ours are, or they haven't yet figured out that the random lockup issue they're seeing originates in the NFS stack. My suspicion is the latter, but time will tell. ----- Original Message ----- > From: "hedrick" <hedrick@xxxxxxxxxxx> > To: "Timothy Pearson" <tpearson@xxxxxxxxxxxxxxxxxxxxx> > Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, "Chuck Lever" <chuck.lever@xxxxxxxxxx>, "linux-nfs" > <linux-nfs@xxxxxxxxxxxxxxx> > Sent: Monday, August 9, 2021 12:15:33 PM > Subject: Re: CPU stall, eventual host hang with BTRFS + NFS under heavy load > There seems to be a soft lockup message on the console, but that’s all I can > find. > > I’m currently considering whether it’s best to move to NFS 4.0, which seems not > to cause the issue, or 4.2 with delegations disabled. This is the primary > server for the department. If it fails, everything fails, VMs because > read-only, user jobs fai, etc. > > We ran for a year before this showed up, so I’m pretty sure going to 4.0 will > fix it. But I have use cases for ACLs that will only work with 4.2. Since the > problem seems to be in the callback mechanism, and as far as I can tell that’s > only used for delegations, I assume turning off delegations will fix it. > > We’ve also had a history of issues with 4.2 problems on clients. That’s why we > backed off to 4.0 initially. Clients were seeing hangs. > > It’s discouraging to hear that even the most recent kernel has problems. > >> On Aug 9, 2021, at 1:06 PM, Timothy Pearson <tpearson@xxxxxxxxxxxxxxxxxxxxx> >> wrote: >> >> Did you see anything else at all on the terminal? The inability to log in is >> sadly familiar, our boxes are configured to dump a trace over serial every 120 >> seconds or so if they lock up (/proc/sys/kernel/hung_task_timeout_secs) and I'm >> not sure you'd see anything past the callback messages without that active. >> >> FWIW we ended up (mostly) working around the problem by moving the critical >> systems (which are all NFSv3) to a new server, but that's a stopgap measure as >> we were looking to deploy NFSv4 on a broader scale. My gut feeling is the >> failure occurs under heavy load where too many NFSv4 requests from a single >> client are pending due to a combination of storage and network saturation, but >> it's proven very difficult to debug -- even splitting the v3 hosts from the >> larger NFS server (reducing traffic + storage load) seems to have temporarily >> stabilized things. >> >> ----- Original Message ----- >>> From: hedrick@xxxxxxxxxxx >>> To: "Timothy Pearson" <tpearson@xxxxxxxxxxxxxxxxxxxxx> >>> Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, "Chuck Lever" >>> <chuck.lever@xxxxxxxxxx>, "linux-nfs" >>> <linux-nfs@xxxxxxxxxxxxxxx> >>> Sent: Monday, August 9, 2021 11:31:25 AM >>> Subject: Re: CPU stall, eventual host hang with BTRFS + NFS under heavy load >> >>> Incidentally, we’re a computer science department. We have such a variety of >>> students and researchers that it’s impossible to know what they are all doing. >>> Historically, if there’s a bug in anyth9ing, we’ll see it, and usually enough >>> for it to be fatal. >>> >>> question: is backing off to 4.0 or disabling delegations likely to have more of >>> an impact on performance? >>> >>>> On Aug 9, 2021, at 12:17 PM, hedrick@xxxxxxxxxxx wrote: >>>> >>>> I just found this because we’ve been dealing with hangs of our primary NFS >>>> server. This is ubuntu 20.04, which is 5.10. >>>> >>>> Right before the hang: >>>> >>>> Aug 8 21:50:46 communis.lcsr.rutgers.edu <http://communis.lcsr.rutgers.edu/> >>>> kernel: [294852.644801] receive_cb_reply: Got unrecognized reply: calldir 0x1 >>>> xpt_bc_xprt 00000000b260cf95 xid e3faa54e >>>> Aug 8 21:51:54 communis.lcsr.rutgers.edu <http://communis.lcsr.rutgers.edu/> >>>> kernel: [294921.252531] receive_cb_reply: Got unrecognized reply: calldir 0x1 >>>> xpt_bc_xprt 00000000b260cf95 xid f0faa54e >>>> >>>> >>>> I looked at the code, and this seems to be an NFS4.1 callback. We just started >>>> seeing the problem after upgrading most of our hosts in a way that caused them >>>> to move from NFS 4.0 to 4.2. I assume 4.2 is using the 4.1 callback. Rather >>>> than disabling delegations, we’re moving back to NFS 4.0 on the clients (except >>>> ESXi). >>>> >>>> We’re using ZFS, so this isn’t just btrfs. >>>> >>>> I’m afraid I don’t have any backtrace. I was going to get more information, but >>>> it happened late at night and we were unable to get into the system to gather >>>> information. Just had to reboot. >>>> >>>>> On Jul 5, 2021, at 5:47 AM, Timothy Pearson <tpearson@xxxxxxxxxxxxxxxxxxxxx >>>>> <mailto:tpearson@xxxxxxxxxxxxxxxxxxxxx>> wrote: >>>>> >>>>> Forgot to add -- sometimes, right before the core stall and backtrace, we see >>>>> messages similar to the following: >>>>> >>>>> [16825.408854] receive_cb_reply: Got unrecognized reply: calldir 0x1 xpt_bc_xprt >>>>> 0000000051f43ff7 xid 2e0c9b7a >>>>> [16825.414070] receive_cb_reply: Got unrecognized reply: calldir 0x1 xpt_bc_xprt >>>>> 0000000051f43ff7 xid 2f0c9b7a >>>>> [16825.414360] receive_cb_reply: Got unrecognized reply: calldir 0x1 xpt_bc_xprt >>>>> 0000000051f43ff7 xid 300c9b7a >>>>> >>>>> We're not sure if they are related or not. >>>>> >>>>> ----- Original Message ----- >>>>>> From: "Timothy Pearson" <tpearson@xxxxxxxxxxxxxxxxxxxxx >>>>>> <mailto:tpearson@xxxxxxxxxxxxxxxxxxxxx>> >>>>>> To: "J. Bruce Fields" <bfields@xxxxxxxxxxxx <mailto:bfields@xxxxxxxxxxxx>>, >>>>>> "Chuck Lever" <chuck.lever@xxxxxxxxxx <mailto:chuck.lever@xxxxxxxxxx>> >>>>>> Cc: "linux-nfs" <linux-nfs@xxxxxxxxxxxxxxx <mailto:linux-nfs@xxxxxxxxxxxxxxx>> >>>>>> Sent: Monday, July 5, 2021 4:44:29 AM >>>>>> Subject: CPU stall, eventual host hang with BTRFS + NFS under heavy load >>>>> >>>>>> We've been dealing with a fairly nasty NFS-related problem off and on for the >>>>>> past couple of years. The host is a large POWER server with several external >>>>>> SAS arrays attached, using BTRFS for cold storage of large amounts of data. >>>>>> The main symptom is that under heavy sustained NFS write traffic using certain >>>>>> file types (see below) a core will suddenly lock up, continually spewing a >>>>>> backtrace similar to the one I've pasted below. While this immediately halts >>>>>> all NFS traffic to the affected client (which is never the same client as the >>>>>> machine doing the large file transfer), the larger issue is that over the next >>>>>> few minutes / hours the entire host will gradually degrade in responsiveness >>>>>> until it grinds to a complete halt. Once the core stall occurs we have been >>>>>> unable to find any way to restore the machine to full functionality or avoid >>>>>> the degradation and eventual hang short of a hard power down and restart. >>>>>> >>>>>> Tens of GB of compressed data in a single file seems to be fairly good at >>>>>> triggering the problem, whereas raw disk images or other regularly patterned >>>>>> data tend not to be. The underlying hardware is functioning perfectly with no >>>>>> problems noted, and moving the files without NFS avoids the bug. >>>>>> >>>>>> We've been using a workaround involving purposefully pausing (SIGSTOP) the file >>>>>> transfer process on the client as soon as other clients start to show a >>>>>> slowdown. This hack avoids the bug entirely provided the host is allowed to >>>>>> catch back up prior to resuming (SIGCONT) the file transfer process. From >>>>>> this, it seems something is going very wrong within the NFS stack under high >>>>>> storage I/O pressure and high storage write latency (timeout?) -- it should >>>>>> simply pause transfers while the storage subsystem catches up, not lock up a >>>>>> core and force a host restart. Interesting, sometimes it does exactly what it >>>>>> is supposed to and does pause and wait for the storage subsystem, but around >>>>>> 20% of the time it just triggers this bug and stalls a core. >>>>>> >>>>>> This bug has been present since at least 4.14 and is still present in the latest >>>>>> 5.12.14 version. >>>>>> >>>>>> As the machine is in production, it is difficult to gather further information >>>>>> or test patches, however we would be able to apply patches to the kernel that >>>>>> would potentially restore stability with enough advance scheduling. >>>>>> >>>>>> Sample backtrace below: >>>>>> >>>>>> [16846.426141] rcu: INFO: rcu_sched self-detected stall on CPU >>>>>> [16846.426202] rcu: 32-....: (5249 ticks this GP) >>>>>> idle=78a/1/0x4000000000000002 softirq=1663878/1663878 fqs=1986 >>>>>> [16846.426241] (t=5251 jiffies g=2720809 q=756724) >>>>>> [16846.426273] NMI backtrace for cpu 32 >>>>>> [16846.426298] CPU: 32 PID: 10624 Comm: kworker/u130:25 Not tainted 5.12.14 #1 >>>>>> [16846.426342] Workqueue: rpciod rpc_async_schedule [sunrpc] >>>>>> [16846.426406] Call Trace: >>>>>> [16846.426429] [c000200010823250] [c00000000074e630] dump_stack+0xc4/0x114 >>>>>> (unreliable) >>>>>> [16846.426483] [c000200010823290] [c00000000075aebc] >>>>>> nmi_cpu_backtrace+0xfc/0x150 >>>>>> [16846.426506] [c000200010823310] [c00000000075b0a8] >>>>>> nmi_trigger_cpumask_backtrace+0x198/0x1f0 >>>>>> [16846.426577] [c0002000108233b0] [c000000000072818] >>>>>> arch_trigger_cpumask_backtrace+0x28/0x40 >>>>>> [16846.426621] [c0002000108233d0] [c000000000202db8] >>>>>> rcu_dump_cpu_stacks+0x158/0x1b8 >>>>>> [16846.426667] [c000200010823470] [c000000000201828] >>>>>> rcu_sched_clock_irq+0x908/0xb10 >>>>>> [16846.426708] [c000200010823560] [c0000000002141d0] >>>>>> update_process_times+0xc0/0x140 >>>>>> [16846.426768] [c0002000108235a0] [c00000000022dd34] >>>>>> tick_sched_handle.isra.18+0x34/0xd0 >>>>>> [16846.426808] [c0002000108235d0] [c00000000022e1e8] tick_sched_timer+0x68/0xe0 >>>>>> [16846.426856] [c000200010823610] [c00000000021577c] >>>>>> __hrtimer_run_queues+0x16c/0x370 >>>>>> [16846.426903] [c000200010823690] [c000000000216378] >>>>>> hrtimer_interrupt+0x128/0x2f0 >>>>>> [16846.426947] [c000200010823740] [c000000000029494] timer_interrupt+0x134/0x310 >>>>>> [16846.426989] [c0002000108237a0] [c000000000016c54] >>>>>> replay_soft_interrupts+0x124/0x2e0 >>>>>> [16846.427045] [c000200010823990] [c000000000016f14] >>>>>> arch_local_irq_restore+0x104/0x170 >>>>>> [16846.427103] [c0002000108239c0] [c00000000017247c] >>>>>> mod_delayed_work_on+0x8c/0xe0 >>>>>> [16846.427149] [c000200010823a20] [c00800000819fe04] >>>>>> rpc_set_queue_timer+0x5c/0x80 [sunrpc] >>>>>> [16846.427234] [c000200010823a40] [c0080000081a096c] >>>>>> __rpc_sleep_on_priority_timeout+0x194/0x1b0 [sunrpc] >>>>>> [16846.427324] [c000200010823a90] [c0080000081a3080] >>>>>> rpc_sleep_on_timeout+0x88/0x110 [sunrpc] >>>>>> [16846.427388] [c000200010823ad0] [c0080000071f7220] nfsd4_cb_done+0x468/0x530 >>>>>> [nfsd] >>>>>> [16846.427457] [c000200010823b60] [c0080000081a0a0c] rpc_exit_task+0x84/0x1d0 >>>>>> [sunrpc] >>>>>> [16846.427520] [c000200010823ba0] [c0080000081a2448] __rpc_execute+0xd0/0x760 >>>>>> [sunrpc] >>>>>> [16846.427598] [c000200010823c30] [c0080000081a2b18] >>>>>> rpc_async_schedule+0x40/0x70 [sunrpc] >>>>>> [16846.427687] [c000200010823c60] [c000000000170bf0] >>>>>> process_one_work+0x290/0x580 >>>>>> [16846.427736] [c000200010823d00] [c000000000170f68] worker_thread+0x88/0x620 >>>>>> [16846.427813] [c000200010823da0] [c00000000017b860] kthread+0x1a0/0x1b0 >>>>>> [16846.427865] [c000200010823e10] [c00000000000d6ec] >>>>>> ret_from_kernel_thread+0x5c/0x70 >>>>>> [16873.869180] watchdog: BUG: soft lockup - CPU#32 stuck for 49s! >>>>>> [kworker/u130:25:10624] >>>>>> [16873.869245] Modules linked in: rpcsec_gss_krb5 iscsi_target_mod >>>>>> target_core_user uio target_core_pscsi target_core_file target_core_iblock >>>>>> target_core_mod tun nft_counter nf_tables nfnetlink vfio_pci vfio_virqfd >>>>>> vfio_iommu_spapr_tce vfio vfio_spapr_eeh i2c_dev bridg$ >>>>>> [16873.869413] linear mlx4_ib ib_uverbs ib_core raid1 md_mod sd_mod t10_pi >>>>>> hid_generic usbhid hid ses enclosure crct10dif_vpmsum crc32c_vpmsum xhci_pci >>>>>> xhci_hcd ixgbe mlx4_core mpt3sas usbcore tg3 mdio_devres of_mdio fixed_phy >>>>>> xfrm_algo mdio libphy aacraid igb raid_cl$ >>>>>> [16873.869889] CPU: 32 PID: 10624 Comm: kworker/u130:25 Not tainted 5.12.14 #1 >>>>>> [16873.869966] Workqueue: rpciod rpc_async_schedule [sunrpc] >>>>>> [16873.870023] NIP: c000000000711300 LR: c0080000081a0708 CTR: c0000000007112a0 >>>>>> [16873.870073] REGS: c0002000108237d0 TRAP: 0900 Not tainted (5.12.14) >>>>>> [16873.870109] MSR: 900000000280b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: >>>>>> 24004842 XER: 00000000 >>>>>> [16873.870146] CFAR: c0080000081d8054 IRQMASK: 0 >>>>>> GPR00: c0080000081a0748 c000200010823a70 c0000000015c0700 c0000000e2227a40 >>>>>> GPR04: c0000000e2227a40 c0000000e2227a40 c000200ffb6cc0a8 0000000000000018 >>>>>> GPR08: 0000000000000000 5deadbeef0000122 c0080000081ffd18 c0080000081d8040 >>>>>> GPR12: c0000000007112a0 c000200fff7fee00 c00000000017b6c8 c000000090d9ccc0 >>>>>> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 >>>>>> GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000040 >>>>>> GPR24: 0000000000000000 0000000000000000 fffffffffffffe00 0000000000000001 >>>>>> GPR28: c00000001a62f000 c0080000081a0988 c0080000081ffd10 c0000000e2227a00 >>>>>> [16873.870452] NIP [c000000000711300] __list_del_entry_valid+0x60/0x100 >>>>>> [16873.870507] LR [c0080000081a0708] > >>>>> rpc_wake_up_task_on_wq_queue_action_locked+0x330/0x400 [sunrpc]
