Re: nfsd hangs and nfsd_break_deleg_cb+0x170/0x190 warning

Charles Hedrick
2024-03-20T13:03:06Z

> On Mar 19, 2024, at 7:36 AM, Jeff Layton <jlayton@kernel.org> wrote:
>
> On Tue, 2024-03-19 at 11:58 +0100, Rik Theys wrote:
>> Hi,
>>
>> On 3/19/24 11:39, Jeff Layton wrote:
>>> On Tue, 2024-03-19 at 08:58 +0100, Rik Theys wrote:
>>>> Hi,
>>>>
>>>> On 3/18/24 22:54, Jeff Layton wrote:
>>>>> On Mon, 2024-03-18 at 22:15 +0100, Rik Theys wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On 3/18/24 21:21, Rik Theys wrote:
>>>>>>> Hi Jeff,
>>>>>>>
>>>>>>> On 3/12/24 13:47, Jeff Layton wrote:
>>>>>>>> On Tue, 2024-03-12 at 13:24 +0100, Rik Theys wrote:
>>>>>>>>> Hi Jeff,
>>>>>>>>>
>>>>>>>>> On 3/12/24 12:22, Jeff Layton wrote:
>>>>>>>>>> On Mon, 2024-03-11 at 19:43 +0100, Rik Theys wrote:
>>>>>>>>>>> Since a few weeks our Rocky Linux 9 NFS server has periodically
>>>>>>>>>>> logged hung nfsd tasks. The initial effect was that some clients
>>>>>>>>>>> could no longer access the NFS server. This got worse and worse
>>>>>>>>>>> (probably as more nfsd threads got blocked) and we had to restart
>>>>>>>>>>> the server. Restarting the server also failed as the NFS server
>>>>>>>>>>> service could no longer be stopped.
>>>>>>>>>>>
>>>>>>>>>>> The initial kernel we noticed this behavior on was
>>>>>>>>>>> kernel-5.14.0-362.18.1.el9_3.x86_64. Since then we've installed
>>>>>>>>>>> kernel-5.14.0-419.el9.x86_64 from CentOS Stream 9. The same issue
>>>>>>>>>>> happened again on this newer kernel version:
>>>>>>>> 419 is fairly up to date with nfsd changes. There are some known bugs
>>>>>>>> around callbacks, and there is a draft MR in flight to fix it.
>>>>>>>>
>>>>>>>> What kernel were you on prior to 5.14.0-362.18.1.el9_3.x86_64 ? If we
>>>>>>>> can bracket the changes around a particular version, then that might
>>>>>>>> help identify the problem.
>>>>>>>>
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] Not tainted 5.14.0-419.el9.x86_64 #1
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] "echo 0 >
>>>>>>>>>>> /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024]task:nfsd state:D stack:0
>>>>>>>>>>> pid:8865 ppid:2 flags:0x00004000
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] Call Trace:
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] <TASK>
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __schedule+0x21b/0x550
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] schedule+0x2d/0x70
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] schedule_timeout+0x11f/0x160
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? select_idle_sibling+0x28/0x430
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? wake_affine+0x62/0x1f0
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __wait_for_common+0x90/0x1d0
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_schedule_timeout+0x10/0x10
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __flush_workqueue+0x13a/0x3f0
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd4_shutdown_callback+0x49/0x120
>>>>>>>>>>> [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? nfsd4_cld_remove+0x54/0x1d0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ?
>>>>>>>>>>> nfsd4_return_all_client_layouts+0xc4/0xf0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? nfsd4_shutdown_copy+0x68/0xc0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __destroy_client+0x1f3/0x290 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd4_exchange_id+0x75f/0x770 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? nfsd4_decode_opaque+0x3a/0x90 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd4_proc_compound+0x44b/0x700 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd_dispatch+0x94/0x1c0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] svc_process_common+0x2ec/0x660
>>>>>>>>>>> [sunrpc]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_nfsd+0x10/0x10 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] svc_process+0x12d/0x170 [sunrpc]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd+0x84/0xb0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] kthread+0xdd/0x100
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_kthread+0x10/0x10
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ret_from_fork+0x29/0x50
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] </TASK>
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] INFO: task nfsd:8866 blocked for
>>>>>>>>>>> more than 122 seconds.
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] Not tainted
>>>>>>>>>>> 5.14.0-419.el9.x86_64 #1
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] "echo 0 >
>>>>>>>>>>> /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024]task:nfsd state:D stack:0
>>>>>>>>>>> pid:8866 ppid:2 flags:0x00004000
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] Call Trace:
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] <TASK>
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __schedule+0x21b/0x550
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] schedule+0x2d/0x70
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] schedule_timeout+0x11f/0x160
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? select_idle_sibling+0x28/0x430
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? tcp_recvmsg+0x196/0x210
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? wake_affine+0x62/0x1f0
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __wait_for_common+0x90/0x1d0
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_schedule_timeout+0x10/0x10
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] __flush_workqueue+0x13a/0x3f0
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd4_destroy_session+0x1a4/0x240
>>>>>>>>>>> [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd4_proc_compound+0x44b/0x700 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd_dispatch+0x94/0x1c0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] svc_process_common+0x2ec/0x660
>>>>>>>>>>> [sunrpc]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_nfsd+0x10/0x10 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] svc_process+0x12d/0x170 [sunrpc]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] nfsd+0x84/0xb0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] kthread+0xdd/0x100
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ? __pfx_kthread+0x10/0x10
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] ret_from_fork+0x29/0x50
>>>>>>>>>>> [Mon Mar 11 14:10:08 2024] </TASK>
>>>>>>>>>>>
>>>>>>>>>> The above threads are trying to flush the workqueue, so that probably
>>>>>>>>>> means that they are stuck waiting on a workqueue job to finish.
>>>>>>>>>>> The above is repeated a few times, and then this warning is
>>>>>>>>>>> also logged:
>>>>>>>>>>> [Mon Mar 11 14:12:04 2024] ------------[ cut here ]------------
>>>>>>>>>>> [Mon Mar 11 14:12:04 2024] WARNING: CPU: 39 PID: 8844 at
>>>>>>>>>>> fs/nfsd/nfs4state.c:4919 nfsd_break_deleg_cb+0x170/0x190 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] Modules linked in: nfsv4
>>>>>>>>>>> dns_resolver nfs fscache netfs rpcsec_gss_krb5 rpcrdma rdma_cm
>>>>>>>>>>> iw_cm ib_cm ib_core binfmt_misc bonding tls rfkill nft_counter nft_ct
>>>>>>>>>>> nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_reject_inet
>>>>>>>>>>> nf_reject_ipv4 nf_reject_ipv6 nft_reject nf_tables nfnetlink vfat
>>>>>>>>>>> fat dm_thin_pool dm_persistent_data dm_bio_prison dm_bufio l
>>>>>>>>>>> ibcrc32c dm_service_time dm_multipath intel_rapl_msr
>>>>>>>>>>> intel_rapl_common intel_uncore_frequency
>>>>>>>>>>> intel_uncore_frequency_common isst_if_common skx_edac nfit
>>>>>>>>>>> libnvdimm ipmi_ssif x86_pkg_temp
>>>>>>>>>>> _thermal intel_powerclamp coretemp kvm_intel kvm irqbypass
>>>>>>>>>>> dcdbas rapl intel_cstate mgag200 i2c_algo_bit drm_shmem_helper
>>>>>>>>>>> dell_smbios drm_kms_helper dell_wmi_descriptor wmi_bmof intel_u
>>>>>>>>>>> ncore syscopyarea pcspkr sysfillrect mei_me sysimgblt acpi_ipmi
>>>>>>>>>>> mei fb_sys_fops i2c_i801 ipmi_si intel_pch_thermal lpc_ich
>>>>>>>>>>> ipmi_devintf i2c_smbus ipmi_msghandler joydev acpi_power_meter
>>>>>>>>>>> nfsd auth_rpcgss nfs_acl drm lockd grace fuse sunrpc ext4
>>>>>>>>>>> mbcache jbd2 sd_mod sg lpfc
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nvmet_fc nvmet nvme_fc nvme_fabrics
>>>>>>>>>>> crct10dif_pclmul ahci libahci crc32_pclmul nvme_core crc32c_intel
>>>>>>>>>>> ixgbe megaraid_sas libata nvme_common ghash_clmulni_int
>>>>>>>>>>> el t10_pi wdat_wdt scsi_transport_fc mdio wmi dca dm_mirror
>>>>>>>>>>> dm_region_hash dm_log dm_mod
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] CPU: 39 PID: 8844 Comm: nfsd Not
>>>>>>>>>>> tainted 5.14.0-419.el9.x86_64 #1
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] Hardware name: Dell Inc. PowerEdge
>>>>>>>>>>> R740/00WGD1, BIOS 2.20.1 09/13/2023
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] RIP:
>>>>>>>>>>> 0010:nfsd_break_deleg_cb+0x170/0x190 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] Code: a6 95 c5 f3 e9 ff fe ff ff 48
>>>>>>>>>>> 89 df be 01 00 00 00 e8 34 b5 13 f4 48 8d bb 98 00 00 00 e8 c8 f9
>>>>>>>>>>> 00 00 84 c0 0f 85 2e ff ff ff <0f> 0b e9 27 ff ff ff be
>>>>>>>>>>> 02 00 00 00 48 89 df e8 0c b5 13 f4 e9 01
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] RSP: 0018:ffff9929e0bb7b80 EFLAGS:
>>>>>>>>>>> 00010246
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] RAX: 0000000000000000 RBX:
>>>>>>>>>>> ffff8ada51930900 RCX: 0000000000000024
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] RDX: ffff8ada519309c8 RSI:
>>>>>>>>>>> ffff8ad582933c00 RDI: 0000000000002000
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] RBP: ffff8ad46bf21574 R08:
>>>>>>>>>>> ffff9929e0bb7b48 R09: 0000000000000000
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] R10: ffff8aec859a2948 R11:
>>>>>>>>>>> 0000000000000000 R12: ffff8ad6f497c360
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] R13: ffff8ad46bf21560 R14:
>>>>>>>>>>> ffff8ae5942e0b10 R15: ffff8ad6f497c360
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] FS: 0000000000000000(0000)
>>>>>>>>>>> GS:ffff8b031fcc0000(0000) knlGS:0000000000000000
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] CS: 0010 DS: 0000 ES: 0000 CR0:
>>>>>>>>>>> 0000000080050033
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] CR2: 00007fafe2060744 CR3:
>>>>>>>>>>> 00000018e58de006 CR4: 00000000007706e0
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] DR0: 0000000000000000 DR1:
>>>>>>>>>>> 0000000000000000 DR2: 0000000000000000
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] DR3: 0000000000000000 DR6:
>>>>>>>>>>> 00000000fffe0ff0 DR7: 0000000000000400
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] PKRU: 55555554
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] Call Trace:
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] <TASK>
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? show_trace_log_lvl+0x1c4/0x2df
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? show_trace_log_lvl+0x1c4/0x2df
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? __break_lease+0x16f/0x5f0
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? nfsd_break_deleg_cb+0x170/0x190
>>>>>>>>>>> [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? __warn+0x81/0x110
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? nfsd_break_deleg_cb+0x170/0x190
>>>>>>>>>>> [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? report_bug+0x10a/0x140
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? handle_bug+0x3c/0x70
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? exc_invalid_op+0x14/0x70
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? asm_exc_invalid_op+0x16/0x20
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? nfsd_break_deleg_cb+0x170/0x190
>>>>>>>>>>> [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] __break_lease+0x16f/0x5f0
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ?
>>>>>>>>>>> nfsd_file_lookup_locked+0x117/0x160 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? list_lru_del+0x101/0x150
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfsd_file_do_acquire+0x790/0x830
>>>>>>>>>>> [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfs4_get_vfs_file+0x315/0x3a0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfsd4_process_open2+0x430/0xa30 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? fh_verify+0x297/0x2f0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfsd4_open+0x3ce/0x4b0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfsd4_proc_compound+0x44b/0x700 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfsd_dispatch+0x94/0x1c0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] svc_process_common+0x2ec/0x660
>>>>>>>>>>> [sunrpc]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? __pfx_nfsd+0x10/0x10 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] svc_process+0x12d/0x170 [sunrpc]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] nfsd+0x84/0xb0 [nfsd]
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] kthread+0xdd/0x100
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ? __pfx_kthread+0x10/0x10
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ret_from_fork+0x29/0x50
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] </TASK>
>>>>>>>>>>> [Mon Mar 11 14:12:05 2024] ---[ end trace 7a039e17443dc651 ]---
>>>>>>>>>> This is probably this WARN in nfsd_break_one_deleg:
>>>>>>>>>>
>>>>>>>>>> WARN_ON_ONCE(!nfsd4_run_cb(&dp->dl_recall));
>>>>>>>>>>
>>>>>>>>>> It means that a delegation break callback to the client couldn't be
>>>>>>>>>> queued to the workqueue, and so it didn't run.
>>>>>>>>>>
>>>>>>>>>>> Could this be the same issue as described
>>>>>>>>>>> here:https://lore.kernel.org/linux-nfs/af0ec881-5ebf-4feb-98ae-3ed2a77f86f1@oracle.com/
>>>>>>>>>>> ?
>>>>>>>>>> Yes, most likely the same problem.
>>>>>>>>> If I read that thread correctly, this issue was introduced between
>>>>>>>>> 6.1.63 and 6.6.3? Is it possible the EL9 5.14.0-362.18.1.el9_3
>>>>>>>>> backported these changes, or were we hitting some other bug with that
>>>>>>>>> version? It seems the 6.1.x kernel is not affected? If so, that
>>>>>>>>> would be
>>>>>>>>> the recommended kernel to run?
>>>>>>>> Anything is possible. We have to identify the problem first.
>>>>>>>>>>> As described in that thread, I've tried to obtain the requested
>>>>>>>>>>> information.
>>>>>>>>>>>
>>>>>>>>>>> Is it possible this is the issue that was fixed by the patches
>>>>>>>>>>> described
>>>>>>>>>>> here?https://lore.kernel.org/linux-nfs/2024022054-cause-suffering-eae8@gregkh/
>>>>>>>>>>>
>>>>>>>>>> Doubtful. Those are targeted toward a different set of issues.
>>>>>>>>>>
>>>>>>>>>> If you're willing, I do have some patches queued up for CentOS here
>>>>>>>>>> that
>>>>>>>>>> fix some backchannel problems that could be related. I'm mainly
>>>>>>>>>> waiting
>>>>>>>>>> on Chuck to send these to Linus and then we'll likely merge them into
>>>>>>>>>> CentOS soon afterward:
>>>>>>>>>>
>>>>>>>>>> https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/3689
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> If you can send me a patch file, I can rebuild the C9S kernel with that
>>>>>>>>> patch and run it. It can take a while for the bug to trigger as I
>>>>>>>>> believe it seems to be very workload dependent (we were running very
>>>>>>>>> stable for months and now hit this bug every other week).
>>>>>>>>>
>>>>>>>>>
>>>>>>>> It's probably simpler to just pull down the build artifacts for that MR.
>>>>>>>> You have to drill down through the CI for it, but they are here:
>>>>>>>>
>>>>>>>> https://s3.amazonaws.com/arr-cki-prod-trusted-artifacts/index.html?prefix=trusted-artifacts/1194300175/publish_x86_64/6278921877/artifacts/
>>>>>>>>
>>>>>>>>
>>>>>>>> There's even a repo file you can install on the box to pull them down.
>>>>>>> We installed this kernel on the server 3 days ago. Today, a user
>>>>>>> informed us that their screen was black after logging in. Similar to
>>>>>>> other occurrences of this issue, the mount command on the client was
>>>>>>> hung. But in contrast to the other times, there were no messages in
>>>>>>> the logs kernel logs on the server. Even restarting the client does
>>>>>>> not resolve the issue.
>>>>> Ok, so you rebooted the client and it's still unable to mount? That
>>>>> sounds like a server problem if so.
>>>>>
>>>>> Are both client and server running the same kernel?
>>>> No, the server runs 5.14.0-427.3689_1194299994.el9 and the client
>>>> 5.14.0-362.18.1.el9_3.
>>> Ok.
>>>
>>>>>>> Something still seems to be wrong on the server though. When I look at
>>>>>>> the directories under /proc/fs/nfsd/clients, there's still a directory
>>>>>>> for the specific client, even though it's no longer running:
>>>>>>>
>>>>>>> # cat 155/info
>>>>>>> clientid: 0xc8edb7f65f4a9ad
>>>>>>> address: "10.87.31.152:819"
>>>>>>> status: confirmed
>>>>>>> seconds from last renew: 33163
>>>>>>> name: "Linux NFSv4.2 bersalis.esat.kuleuven.be"
>>>>>>> minor version: 2
>>>>>>> Implementation domain: "kernel.org"
>>>>>>> Implementation name: "Linux 5.14.0-362.18.1.el9_3.0.1.x86_64 #1 SMP
>>>>>>> PREEMPT_DYNAMIC Sun Feb 11 13:49:23 UTC 2024 x86_64"
>>>>>>> Implementation time: [0, 0]
>>>>>>> callback state: DOWN
>>>>>>> callback address: 10.87.31.152:0
>>>>>>>
>>>>> If you just shut down the client, the server won't immediately purge its
>>>>> record. In fact, assuming you're running the same kernel on the server,
>>>>> it won't purge the client record until there is a conflicting request
>>>>> for its state.
>>>> Is there a way to force such a conflicting request (to get the client
>>>> record to purge)?
>>> From the server or a different client, you can try opening the inodes
>>> that the stuck client is holding open. If you open them for write, that
>>> may trigger the server to kick out the old client record.
>>>
>>> The problem is that they are disconnected dentries, so finding them to
>>> open via path may be difficult...
>>
>> I've located the file that matches one of these inodes. When I go to the
>>
>> location of the file on another NFS client and touch the file, the touch
>> command
>>
>> just hangs.
>>
>> So I assume the server is trying to recall the delegation from the
>> dis-functional client?
>>
>> When I run tcpdump on the dis-functional client, I see the
>> CREATE_SESSION / NFS4ERR_DELAY messages, but nothing to indicate the
>> server wants to revoke a delegation.
>>
>
> Right, according to the client record above, the callback channel is
> DOWN, so the server can't communicate with the client. Given that there
> are 33000s since the last lease renewal, the server should kick the
> client out that is blocking other activity, but that doesn't seem to be
> happening here.
>
>
>> The entry for the dis-functional client is not removed on the server.
>>
>> I there anything else I can do to provide more information about this
>> situation?
>>
>>
>
> The main function that handles the CREATE_SESSION call is
> nfsd4_create_session. It's somewhat complex and there are a number of
> reasons that function could return NFS4ERR_DELAY (aka nfserr_jukebox in
> the kernel code).
>
> What I'd do at this point is turn up tracepoints and see whether they
> shed any light on what's going wrong to make it continually delay your
> CREATE_SESSION calls. There aren't a lot of tracepoints in that code,
> however, so it may not show much.
>
> In the absence of that, you can try to use bpftrace or something similar
> to debug what's happening in that function.
>
>>
>>
>>>>>> The nfsdclnts command for this client shows the following delegations:
>>>>>>
>>>>>> # nfsdclnts -f 155/states -t all
>>>>>> Inode number | Type | Access | Deny | ip address | Filename
>>>>>> 169346743 | open | r- | -- | 10.87.31.152:819 |
>>>>>> disconnected dentry
>>>>>> 169346743 | deleg | r | | 10.87.31.152:819 |
>>>>>> disconnected dentry
>>>>>> 169346746 | open | r- | -- | 10.87.31.152:819 |
>>>>>> disconnected dentry
>>>>>> 169346746 | deleg | r | | 10.87.31.152:819 |
>>>>>> disconnected dentry
>>>>>>
>>>>>> I see a lot of recent patches regarding directory delegations. Could
>>>>>> this be related to this?
>>>>>>
>>>>>> Will a 5.14.0-362.18.1.el9_3.0.1 kernel try to use a directory delegation?
>>>>>>
>>>>>>
>>>>> No. Directory delegations are a new feature that's still under
>>>>> development. They use some of the same machinery as file delegations,
>>>>> but they wouldn't be a factor here.
>>>>>
>>>>>>> The system seems to have identified that the client is no longer
>>>>>>> reachable, but the client entry does not go away. When a mount was
>>>>>>> hanging on the client, there would be two directories in clients for
>>>>>>> the same client. Killing the mount command clears up the second entry.
>>>>>>>
>>>>>>> Even after running conntrack -D on the server to remove the tcp
>>>>>>> connection from the conntrack table, the entry doesn't go away and the
>>>>>>> client still can not mount anything from the server.
>>>>>>>
>>>>>>> A tcpdump on the client while a mount was running logged the following
>>>>>>> messages over and over again:
>>>>>>>
>>>>>>> request:
>>>>>>>
>>>>>>> Frame 1: 378 bytes on wire (3024 bits), 378 bytes captured (3024 bits)
>>>>>>> Ethernet II, Src: HP_19:7d:4b (e0:73:e7:19:7d:4b), Dst:
>>>>>>> ArubaaHe_f9:8e:00 (88:3a:30:f9:8e:00)
>>>>>>> Internet Protocol Version 4, Src: 10.87.31.152, Dst: 10.86.18.14
>>>>>>> Transmission Control Protocol, Src Port: 932, Dst Port: 2049, Seq: 1,
>>>>>>> Ack: 1, Len: 312
>>>>>>> Remote Procedure Call, Type:Call XID:0x1d3220c4
>>>>>>> Network File System
>>>>>>> [Program Version: 4]
>>>>>>> [V4 Procedure: COMPOUND (1)]
>>>>>>> GSS Data, Ops(1): CREATE_SESSION
>>>>>>> Length: 152
>>>>>>> GSS Sequence Number: 76
>>>>>>> Tag: <EMPTY>
>>>>>>> minorversion: 2
>>>>>>> Operations (count: 1): CREATE_SESSION
>>>>>>> [Main Opcode: CREATE_SESSION (43)]
>>>>>>> GSS Checksum:
>>>>>>> 00000028040404ffffffffff000000002c19055f1f8d442d594c13849628affc2797cbb2…
>>>>>>> GSS Token Length: 40
>>>>>>> GSS-API Generic Security Service Application Program Interface
>>>>>>> krb5_blob:
>>>>>>> 040404ffffffffff000000002c19055f1f8d442d594c13849628affc2797cbb23fa080b0…
>>>>>>>
>>>>>>> response:
>>>>>>>
>>>>>>> Frame 2: 206 bytes on wire (1648 bits), 206 bytes captured (1648 bits)
>>>>>>> Ethernet II, Src: ArubaaHe_f9:8e:00 (88:3a:30:f9:8e:00), Dst:
>>>>>>> HP_19:7d:4b (e0:73:e7:19:7d:4b)
>>>>>>> Internet Protocol Version 4, Src: 10.86.18.14, Dst: 10.87.31.152
>>>>>>> Transmission Control Protocol, Src Port: 2049, Dst Port: 932, Seq: 1,
>>>>>>> Ack: 313, Len: 140
>>>>>>> Remote Procedure Call, Type:Reply XID:0x1d3220c4
>>>>>>> Network File System
>>>>>>> [Program Version: 4]
>>>>>>> [V4 Procedure: COMPOUND (1)]
>>>>>>> GSS Data, Ops(1): CREATE_SESSION(NFS4ERR_DELAY)
>>>>>>> Length: 24
>>>>>>> GSS Sequence Number: 76
>>>>>>> Status: NFS4ERR_DELAY (10008)
>>>>>>> Tag: <EMPTY>
>>>>>>> Operations (count: 1)
>>>>>>> [Main Opcode: CREATE_SESSION (43)]
>>>>>>> GSS Checksum:
>>>>>>> 00000028040405ffffffffff000000000aa742d0798deaad1a8aa2d7c3a91bf4f6274222…
>>>>>>> GSS Token Length: 40
>>>>>>> GSS-API Generic Security Service Application Program Interface
>>>>>>> krb5_blob:
>>>>>>> 040405ffffffffff000000000aa742d0798deaad1a8aa2d7c3a91bf4f627422226d74923…
>>>>>>>
>>>>>>> I was hoping that giving the client a different IP address would
>>>>>>> resolve the issue for this client, but it didn't. Even though the
>>>>>>> client had a new IP address (hostname was kept the same), it failed to
>>>>>>> mount anything from the server.
>>>>>>>
>>>>> Changing the IP address won't help. The client is probably using the
>>>>> same long-form client id as before, so the server still identifies the
>>>>> client even with the address change.
>>>> How is the client id determined? Will changing the hostname of the
>>>> client trigger a change of the client id?
>>> In the client record you showed a bit above, there is a "name" field:
>>>
>>> name: "Linux NFSv4.2 bersalis.esat.kuleuven.be"
>>>
>>> That's the string the server uses to uniquely identify the client. So
>>> yes, changing the hostname should change that string.
>>>
>>>>> Unfortunately, the cause of an NFS4ERR_DELAY error is tough to guess.
>>>>> The client is expected to back off and retry, so if the server keeps
>>>>> returning that repeatedly, then a hung mount command is expected.
>>>>>
>>>>> The question is why the server would keep returning DELAY. A lot of
>>>>> different problems ranging from memory allocation issues to protocol
>>>>> problems can result in that error. You may want to check the NFS server
>>>>> and see if anything was logged there.
>>>> There are no messages in the system logs that indicate any sort of
>>>> memory issue. We also increased the min_kbytes_free sysctl to 2G on the
>>>> server before we restarted it with the newer kernel.
>>> Ok, I didn't expect to see anything like that, but it was a possibility.
>>>
>>>>> This is on a CREATE_SESSION call, so I wonder if the record held by the
>>>>> (courteous) server is somehow blocking the attempt to reestablish the
>>>>> session?
>>>>>
>>>>> Do you have a way to reproduce this? Since this is a centos kernel, you
>>>>> could follow the page here to open a bug:
>>>> Unfortunately we haven't found a reliable way to reproduce it. But we do
>>>> seem to trigger it more and more lately.
>>>>
>>>>
>>> Bummer, ok. Let us know if you figure out a way to reproduce it.
>>>
>>>>> https://wiki.centos.org/ReportBugs.html
>>>>>
>>>>>
>>>>>>> I created another dump of the workqueues and worker pools on the server:
>>>>>>>
>>>>>>> [Mon Mar 18 14:59:33 2024] Showing busy workqueues and worker pools:
>>>>>>> [Mon Mar 18 14:59:33 2024] workqueue events: flags=0x0
>>>>>>> [Mon Mar 18 14:59:33 2024] pwq 54: cpus=27 node=1 flags=0x0 nice=0
>>>>>>> active=1/256 refcnt=2
>>>>>>> [Mon Mar 18 14:59:33 2024] pending: drm_fb_helper_damage_work
>>>>>>> [drm_kms_helper]
>>>>>>> [Mon Mar 18 14:59:33 2024] workqueue events_power_efficient: flags=0x80
>>>>>>> [Mon Mar 18 14:59:33 2024] pwq 54: cpus=27 node=1 flags=0x0 nice=0
>>>>>>> active=1/256 refcnt=2
>>>>>>> [Mon Mar 18 14:59:33 2024] pending: fb_flashcursor
>>>>>>> [Mon Mar 18 14:59:33 2024] workqueue mm_percpu_wq: flags=0x8
>>>>>>> [Mon Mar 18 14:59:33 2024] pwq 54: cpus=27 node=1 flags=0x0 nice=0
>>>>>>> active=1/256 refcnt=3
>>>>>>> [Mon Mar 18 14:59:33 2024] pending: lru_add_drain_per_cpu BAR(362)
>>>>>>> [Mon Mar 18 14:59:33 2024] workqueue kblockd: flags=0x18
>>>>>>> [Mon Mar 18 14:59:33 2024] pwq 55: cpus=27 node=1 flags=0x0 nice=-20
>>>>>>> active=1/256 refcnt=2
>>>>>>> [Mon Mar 18 14:59:33 2024] pending: blk_mq_timeout_work
>>>>>>>
>>>>>>>
>>>>>>> In contrast to last time, it doesn't show anything regarding nfs this
>>>>>>> time.
>>>>>>>
>>>>>>> I also tried the suggestion from Dai Ngo (echo 3 >
>>>>>>> /proc/sys/vm/drop_caches), but that didn't seem to make any difference.
>>>>>>>
>>>>>>> We haven't restarted the server yet as it seems the impact seems to
>>>>>>> affect fewer clients that before. Is there anything we can run on the
>>>>>>> server to further debug this?
>>>>>>>
>>>>>>> In the past, the issue seemed to deteriorate rapidly and resulted in
>>>>>>> issues for almost all clients after about 20 minutes. This time the
>>>>>>> impact seems to be less, but it's not gone.
>>>>>>>
>>>>>>> How can we force the NFS server to forget about a specific client? I
>>>>>>> haven't tried to restart the nfs service yet as I'm afraid it will
>>>>>>> fail to stop as before.
>>>>>>>
>>>>> Not with that kernel. There are some new administrative interfaces that
>>>>> might allow that in the future, but they were just merged upstream and
>>>>> aren't in that kernel.
>>>>>
>>>>> --
>>>>> Jeff Layton <jlayton@kernel.org>
>>
>
> --
> Jeff Layton <jlayton@kernel.org>

For years we’ve seen hangs with NFS4 on one particular server. The symptoms look precisely like this. Rebooting the client doesn’t help. Echo expire hangs. I haven’t been able to get a usable backtrace. What’s characteristic of this server is that delegations are off but there’s a high rate of locking and unlocking. Could that cause the same problem?

I’d be happy to collect data if you can suggest a way. Typical traces aren’t going to be useful unless they are very specific, because this is a very busy server, which we can’t take down for debugging.
>