Re: nfsd blocks indefinitely in nfsd4_destroy_session

Baptiste PELLEGRIN
2025-01-14T20:31:52Z

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On 09/01/25 17:32, Chuck Lever <chuck.lever@oracle.com> wrote:
> On 1/9/25 7:42 AM, Jeff Layton wrote:
> >On Thu, 2025-01-09 at 12:56 +0100, Christian Herzog wrote:
> >>Dear Chuck,
> >>
> >>On Wed, Jan 08, 2025 at 10:07:49AM -0500, Chuck Lever wrote:
> >>>On 1/8/25 9:54 AM, Christian Herzog wrote:
> >>>>Dear Chuck,
> >>>>
> >>>>On Wed, Jan 08, 2025 at 08:33:23AM -0500, Chuck Lever wrote:
> >>>>>On 1/7/25 4:17 PM, Salvatore Bonaccorso wrote:
> >>>>>>Hi Chuck,
> >>>>>>
> >>>>>>Thanks for your time on this, much appreciated.
> >>>>>>
> >>>>>>On Wed, Jan 01, 2025 at 02:24:50PM -0500, Chuck Lever wrote:
> >>>>>>>On 12/25/24 4:15 AM, Salvatore Bonaccorso wrote:
> >>>>>>>>Hi Chuck, hi all,
> >>>>>>>>
> >>>>>>>>[it was not ideal to pick one of the message for this
followup, let me
> >>>>>>>>know if you want a complete new thread, adding as well
Benjamin and
> >>>>>>>>Trond as they are involved in one mentioned patch]
> >>>>>>>>
> >>>>>>>>On Mon, Jun 17, 2024 at 02:31:54PM +0000, Chuck Lever III wrote:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>>On Jun 17, 2024, at 2:55 AM, Harald Dunkel
<harald.dunkel@aixigo.com> wrote:
> >>>>>>>>>>
> >>>>>>>>>>Hi folks,
> >>>>>>>>>>
> >>>>>>>>>>what would be the reason for nfsd getting stuck somehow and
becoming
> >>>>>>>>>>an unkillable process? See
> >>>>>>>>>>
> >>>>>>>>>>- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1071562
> >>>>>>>>>>-
https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/2062568
> >>>>>>>>>>
> >>>>>>>>>>Doesn't this mean that something inside the kernel gets
stuck as
> >>>>>>>>>>well? Seems odd to me.
> >>>>>>>>>
> >>>>>>>>>I'm not familiar with the Debian or Ubuntu kernel packages. Can
> >>>>>>>>>the kernel release numbers be translated to LTS kernel releases
> >>>>>>>>>please? Need both "last known working" and "first broken"
releases.
> >>>>>>>>>
> >>>>>>>>>This:
> >>>>>>>>>
> >>>>>>>>>[ 6596.911785] RPC: Could not send backchannel reply error: -110
> >>>>>>>>>[ 6596.972490] RPC: Could not send backchannel reply error: -110
> >>>>>>>>>[ 6837.281307] RPC: Could not send backchannel reply error: -110
> >>>>>>>>>
> >>>>>>>>>is a known set of client backchannel bugs. Knowing the LTS
kernel
> >>>>>>>>>releases (see above) will help us figure out what needs to be
> >>>>>>>>>backported to the LTS kernels kernels in question.
> >>>>>>>>>
> >>>>>>>>>This:
> >>>>>>>>>
> >>>>>>>>>[11183.290619] wait_for_completion+0x88/0x150
> >>>>>>>>>[11183.290623] __flush_workqueue+0x140/0x3e0
> >>>>>>>>>[11183.290629] nfsd4_probe_callback_sync+0x1a/0x30 [nfsd]
> >>>>>>>>>[11183.290689] nfsd4_destroy_session+0x186/0x260 [nfsd]
> >>>>>>>>>
> >>>>>>>>>is probably related to the backchannel errors on the client, but
> >>>>>>>>>client bugs shouldn't cause the server to hang like this. We
> >>>>>>>>>might be able to say more if you can provide the kernel release
> >>>>>>>>>translations (see above).
> >>>>>>>>
> >>>>>>>>In Debian we hstill have the bug #1071562 open and one person
notified
> >>>>>>>>mye offlist that it appears that the issue get more frequent
since
> >>>>>>>>they updated on NFS client side from Ubuntu 20.04 to Debian
bookworm
> >>>>>>>>with a 6.1.y based kernel).
> >>>>>>>>
> >>>>>>>>Some people around those issues, seem to claim that the change
> >>>>>>>>mentioned in
>
>>>>>>>>https://lists.proxmox.com/pipermail/pve-devel/2024-July/064614.html
> >>>>>>>>would fix the issue, which is as well backchannel related.
> >>>>>>>>
> >>>>>>>>This is upstream: 6ddc9deacc13 ("SUNRPC: Fix backchannel reply,
> >>>>>>>>again"). While this commit fixes 57331a59ac0d ("NFSv4.1: Use the
> >>>>>>>>nfs_client's rpc timeouts for backchannel") this is not something
> >>>>>>>>which goes back to 6.1.y, could it be possible that hte
backchannel
> >>>>>>>>refactoring and this final fix indeeds fixes the issue?
> >>>>>>>>
> >>>>>>>>As people report it is not easily reproducible, so this makes it
> >>>>>>>>harder to identify fixes correctly.
> >>>>>>>>
> >>>>>>>>I gave a (short) stance on trying to backport commits up to
> >>>>>>>>6ddc9deacc13 ("SUNRPC: Fix backchannel reply, again") but
this quickly
> >>>>>>>>seems to indicate it is probably still not the right thing for
> >>>>>>>>backporting to the older stable series.
> >>>>>>>>
> >>>>>>>>As at least pre-requisites:
> >>>>>>>>
> >>>>>>>>2009e32997ed568a305cf9bc7bf27d22e0f6ccda
> >>>>>>>>4119bd0306652776cb0b7caa3aea5b2a93aecb89
> >>>>>>>>163cdfca341b76c958567ae0966bd3575c5c6192
> >>>>>>>>f4afc8fead386c81fda2593ad6162271d26667f8
> >>>>>>>>6ed8cdf967f7e9fc96cd1c129719ef99db2f9afc
> >>>>>>>>57331a59ac0d680f606403eb24edd3c35aecba31
> >>>>>>>>
> >>>>>>>>and still there would be conflicting codepaths (and does not seem
> >>>>>>>>right).
> >>>>>>>>
> >>>>>>>>Chuck, Benjamin, Trond, is there anything we can provive on
reporters
> >>>>>>>>side that we can try to tackle this issue better?
> >>>>>>>
> >>>>>>>As I've indicated before, NFSD should not block no matter what the
> >>>>>>>client may or may not be doing. I'd like to focus on the
server first.
> >>>>>>>
> >>>>>>>What is the result of:
> >>>>>>>
> >>>>>>>$ cd <Bookworm's v6.1.90 kernel source >
> >>>>>>>$ unset KBUILD_OUTPUT
> >>>>>>>$ make -j `nproc`
> >>>>>>>$ scripts/faddr2line \
> >>>>>>> fs/nfsd/nfs4state.o \
> >>>>>>> nfsd4_destroy_session+0x16d
> >>>>>>>
> >>>>>>>Since this issue appeared after v6.1.1, is it possible to bisect
> >>>>>>>between v6.1.1 and v6.1.90 ?
> >>>>>>
> >>>>>>First please note, at least speaking of triggering the issue in
> >>>>>>Debian, Debian has moved to 6.1.119 based kernel already (and
soon in
> >>>>>>the weekends point release move to 6.1.123).
> >>>>>>
> >>>>>>That said, one of the users which regularly seems to be hit by the
> >>>>>>issue was able to provide the above requested information,
based for
> >>>>>>6.1.119:
> >>>>>>
> >>>>>>~/kernel/linux-source-6.1# make kernelversion
> >>>>>>6.1.119
> >>>>>>~/kernel/linux-source-6.1# scripts/faddr2line
fs/nfsd/nfs4state.o nfsd4_destroy_session+0x16d
> >>>>>>nfsd4_destroy_session+0x16d/0x250:
> >>>>>>__list_del_entry at
/root/kernel/linux-source-6.1/./include/linux/list.h:134
> >>>>>>(inlined by) list_del at
/root/kernel/linux-source-6.1/./include/linux/list.h:148
> >>>>>>(inlined by) unhash_session at
/root/kernel/linux-source-6.1/fs/nfsd/nfs4state.c:2062
> >>>>>>(inlined by) nfsd4_destroy_session at
/root/kernel/linux-source-6.1/fs/nfsd/nfs4state.c:3856
> >>>>>>
> >>>>>>They could provide as well a decode_stacktrace output for the
recent
> >>>>>>hit (if that is helpful for you):
> >>>>>>
> >>>>>>[Mon Jan 6 13:25:28 2025] INFO: task nfsd:55306 blocked for
more than 6883 seconds.
> >>>>>>[Mon Jan 6 13:25:28 2025] Not tainted 6.1.0-28-amd64 #1
Debian 6.1.119-1
> >>>>>>[Mon Jan 6 13:25:28 2025] "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >>>>>>[Mon Jan 6 13:25:28 2025] task:nfsd state:D stack:0
pid:55306 ppid:2 flags:0x00004000
> >>>>>>[Mon Jan 6 13:25:28 2025] Call Trace:
> >>>>>>[Mon Jan 6 13:25:28 2025] <TASK>
> >>>>>>[Mon Jan 6 13:25:28 2025] __schedule+0x34d/0x9e0
> >>>>>>[Mon Jan 6 13:25:28 2025] schedule+0x5a/0xd0
> >>>>>>[Mon Jan 6 13:25:28 2025] schedule_timeout+0x118/0x150
> >>>>>>[Mon Jan 6 13:25:28 2025] wait_for_completion+0x86/0x160
> >>>>>>[Mon Jan 6 13:25:28 2025] __flush_workqueue+0x152/0x420
> >>>>>>[Mon Jan 6 13:25:28 2025] nfsd4_destroy_session
(debian/build/build_amd64_none_amd64/include/linux/spinlock.h:351
debian/build/build_amd64_none_amd64/fs/nfsd/nfs4state.c:3861) nfsd
> >>>>>>[Mon Jan 6 13:25:28 2025] nfsd4_proc_compound
(debian/build/build_amd64_none_amd64/fs/nfsd/nfs4proc.c:2680) nfsd
> >>>>>>[Mon Jan 6 13:25:28 2025] nfsd_dispatch
(debian/build/build_amd64_none_amd64/fs/nfsd/nfssvc.c:1022) nfsd
> >>>>>>[Mon Jan 6 13:25:28 2025] svc_process_common
(debian/build/build_amd64_none_amd64/net/sunrpc/svc.c:1344) sunrpc
> >>>>>>[Mon Jan 6 13:25:28 2025] ? svc_recv
(debian/build/build_amd64_none_amd64/net/sunrpc/svc_xprt.c:897) sunrpc
> >>>>>>[Mon Jan 6 13:25:28 2025] ? nfsd_svc
(debian/build/build_amd64_none_amd64/fs/nfsd/nfssvc.c:983) nfsd
> >>>>>>[Mon Jan 6 13:25:28 2025] ? nfsd_inet6addr_event
(debian/build/build_amd64_none_amd64/fs/nfsd/nfssvc.c:922) nfsd
> >>>>>>[Mon Jan 6 13:25:28 2025] svc_process
(debian/build/build_amd64_none_amd64/net/sunrpc/svc.c:1474) sunrpc
> >>>>>>[Mon Jan 6 13:25:28 2025] nfsd
(debian/build/build_amd64_none_amd64/fs/nfsd/nfssvc.c:960) nfsd
> >>>>>>[Mon Jan 6 13:25:28 2025] kthread+0xd7/0x100
> >>>>>>[Mon Jan 6 13:25:28 2025] ? kthread_complete_and_exit+0x20/0x20
> >>>>>>[Mon Jan 6 13:25:28 2025] ret_from_fork+0x1f/0x30
> >>>>>>[Mon Jan 6 13:25:28 2025] </TASK>
> >>>>>>
> >>>>>>The question about bisection is actually harder, those are
production
> >>>>>>systems and I understand it's not possible to do bisect there,
while
> >>>>>>unfortunately not reprodcing the issue on "lab conditions".
> >>>>>>
> >>>>>>Does the above give us still a clue on what you were looking for?
> >>>>>
> >>>>>Thanks for the update.
> >>>>>
> >>>>>It's possible that 38f080f3cd19 ("NFSD: Move callback_wq into struct
> >>>>>nfs4_client"), while not a specific fix for this issue, might
offer some
> >>>>>relief by preventing the DESTROY_SESSION hang from affecting all
other
> >>>>>clients of the degraded server.
> >>>>>
> >>>>>Not having a reproducer or the ability to bisect puts a damper on
> >>>>>things. The next step, then, is to enable tracing on servers
where this
> >>>>>issue can come up, and wait for the hang to occur. The following
command
> >>>>>captures information only about callback operation, so it should not
> >>>>>generate much data or impact server performance.
> >>>>>
> >>>>> # trace-cmd record -e nfsd:nfsd_cb\*
> >>>>>
> >>>>>Let that run until the problem occurs, then ^C, compress the
resulting
> >>>>>trace.dat file, and either attach it to 1071562 or email it to me
> >>>>>privately.
> >>>>thanks for the follow-up.
> >>>>
> >>>>I am the "customer" with two affected file servers. We have since
moved those
> >>>>servers to the backports kernel (6.11.10) in the hope of forward
fixing the
> >>>>issue. If this kernel is stable, I'm afraid I can't go back to
the 'bad'
> >>>>kernel (700+ researchers affected..), and we're also not able to
trigger the
> >>>>issue on our test environment.
> >>>
> >>>Hello Dr. Herzog -
> >>>
> >>>If the problem recurs on 6.11, the trace-cmd I suggest above works
> >>>there as well.
> >>the bad news is: it just happened again with the bpo kernel.
> >>
> >>We then immediately started trace-cmd since usually there are
several call
> >>traces in a row and we did get a trace.dat:
> >>http://people.phys.ethz.ch/~daduke/trace.dat
> >>
> >>we did notice however that the stack trace looked a bit different
this time:
> >>
> >> INFO: task nfsd:2566 blocked for more than 5799 seconds.
> >> Tainted: G W 6.11.10+bpo-amd64 #1 Debia>
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables t>
> >> task:nfsd state:D stack:0 pid:2566 tgid:2566 >
> >> Call Trace:
> >> <TASK>
> >> __schedule+0x400/0xad0
> >> schedule+0x27/0xf0
> >> nfsd4_shutdown_callback+0xfe/0x140 [nfsd]
> >> ? __pfx_var_wake_function+0x10/0x10
> >> __destroy_client+0x1f0/0x290 [nfsd]
> >> nfsd4_destroy_clientid+0xf1/0x1e0 [nfsd]
> >> ? svcauth_unix_set_client+0x586/0x5f0 [sunrpc]
> >> nfsd4_proc_compound+0x34d/0x670 [nfsd]
> >> nfsd_dispatch+0xfd/0x220 [nfsd]
> >> svc_process_common+0x2f7/0x700 [sunrpc]
> >> ? __pfx_nfsd_dispatch+0x10/0x10 [nfsd]
> >> svc_process+0x131/0x180 [sunrpc]
> >> svc_recv+0x830/0xa10 [sunrpc]
> >> ? __pfx_nfsd+0x10/0x10 [nfsd]
> >> nfsd+0x87/0xf0 [nfsd]
> >> kthread+0xcf/0x100
> >> ? __pfx_kthread+0x10/0x10
> >> ret_from_fork+0x31/0x50
> >> ? __pfx_kthread+0x10/0x10
> >> ret_from_fork_asm+0x1a/0x30
> >> </TASK>
> >>
> >>and also the state of the offending client in
`/proc/fs/nfsd/clients/*/info`
> >>used to be callback state: UNKNOWN while now it is DOWN or FAULT.
No idea
> >>what it means, but I thought it was worth mentioning.
> >>
> >
> >Looks like this is hung in nfsd41_cb_inflight_wait_complete() ? That
> >probably means that the cl_cb_inflight counter is stuck at >0. I'm
> >guessing that means that there is some callback that it's expecting to
> >complete that isn't. From nfsd4_shutdown_callback():
> >
> > /*
> > * Note this won't actually result in a null callback;
> > * instead, nfsd4_run_cb_null() will detect the killed
> > * client, destroy the rpc client, and stop:
> > */
> > nfsd4_run_cb(&clp->cl_cb_null);
> > flush_workqueue(clp->cl_callback_wq);
> > nfsd41_cb_inflight_wait_complete(clp);
> >
> >...it sounds like that isn't happening properly though.
> >
> >It might be interesting to see if you can track down the callback
> >client in /sys/kernel/debug/sunrpc and see what it's doing.
>
> Here's a possible scenario:
>
> The trace.dat shows the server is sending a lot of CB_RECALL_ANY
> operations.
>
> Normally a callback occurs only due to some particular client request.
> Such requests would be completed before a client unmounts.
>
> CB_RECALL_ANY is an operation which does not occur due to a particular
> client operation and can occur at any time. I believe this is the
> first operation of this type we've added to NFSD.
>
> My guess is that the server's laundromat has sent some CB_RECALL_ANY
> operations while the client is umounting -- DESTROY_SESSION is
> racing with those callback operations.
>
> deleg_reaper() was backported to 6.1.y in 6.1.81, which lines up
> more or less with when the issues started to show up.
>
> A quick way to test this theory would be to make deleg_reaper() a
> no-op. If this helps, then we know that shutting down the server's
> callback client needs to be more careful about cleaning up outstanding
> callbacks.
>
>
> --
> Chuck Lever

Hello !

Got It !

Strangely today my two NFS servers hangs "almost" simultaneously :

One the Jan 14 at 09:14
One the Jan 14 at 10:14

The kernel record is in attachment with my syslog.

Here some additional info :

I my case, during the high school working time, the crash occur the same
day every week, but the hour vary. After a vacation period the day of
the week change but stay the same during the working period.

On September the crash was every Monday.
On December the crash was every Friday.
And now the crash occur every Tuesday.

So I suspect that some log rotation or automated Weekly job on the
client side produce the problem. I can't find anything on the server
side checking systemd timers.

Rebooting the server the morning before the "planned" crash avoid
generally the hang... very strange.

Thanks a lot !

Regards,

Baptiste.

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