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From:   Mike Javorski <mike.javorski@gmail.com>
Date:   Mon, 9 Aug 2021 17:50:08 -0700
Message-ID: <CAOv1SKCUM5cGuXWAc7dsXtbmPMATqd245juC+S9gVXHWiZsvmQ@mail.gmail.com>
Subject: Re: NFS server regression in kernel 5.13 (tested w/ 5.13.9)
To:     linux-nfs@vger.kernel.org
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Managed to get the rpcdebug info for some freezes today. I had a loop
running to call the rpcbind command that Neil provided and then sleep
for 2 seconds. Each triggering event was the opening of a new video
file (I was shuffling through files with mpv). I haven't managed to
get a tcp capture yet trying to get one that isn't too massive, but
the timing is tricky, and this doesn't happen every time.

-----------------------------

[31229.965368] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31229.965370] 44224 c801      0 8c478d70 2473aa3b    15395  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31229.965411] 44225 c801      0 8c478d70 a7d3b9b8    15395  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31231.966982] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31231.966986] 44224 c801      0 8c478d70 2473aa3b    14795  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31231.967027] 44225 c801      0 8c478d70 a7d3b9b8    14795  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31233.968741] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31233.968745] 44224 c801      0 8c478d70 2473aa3b    14194  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31233.968787] 44225 c801      0 8c478d70 a7d3b9b8    14194  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending

-----------------------------

[31292.534529] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31292.534530] 45744 c801      0 8c478d70 2473aa3b    15340  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31292.534554] 45745 c801      0 8c478d70 50cbef7b    15342  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31294.536203] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31294.536206] 45744 c801      0 8c478d70 2473aa3b    14740  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31294.536232] 45745 c801      0 8c478d70 50cbef7b    14742  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31296.537826] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31296.537830] 45744 c801      0 8c478d70 2473aa3b    14139  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31296.537871] 45745 c801      0 8c478d70 50cbef7b    14141  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31298.539474] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31298.539478] 45744 c801      0 8c478d70 2473aa3b    13539  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31298.539522] 45745 c801      0 8c478d70 50cbef7b    13541  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31300.541040] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31300.541044] 46048 c801      0 8c478d70 50cbef7b    17965  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31300.541108] 46049 c801      0 8c478d70 2473aa3b    17965  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31302.542632] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31302.542635] 46922 c801      0 8c478d70 50cbef7b    18000  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending

---------------------------

[31375.046020] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31375.046022] 47336 c801      0 8c478d70 cebaa9a6    15964  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31375.046048] 47337 c801      0 8c478d70 f7145d4d    15964  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31377.047361] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31377.047365] 47336 c801      0 8c478d70 cebaa9a6    15364  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31377.047406] 47337 c801      0 8c478d70 f7145d4d    15364  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31379.048801] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31379.048805] 47336 c801      0 8c478d70 cebaa9a6    14764  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31379.048845] 47337 c801      0 8c478d70 f7145d4d    14764  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31381.050376] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31381.050380] 47336 c801      0 8c478d70 cebaa9a6    14163  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31381.050421] 47337 c801      0 8c478d70 f7145d4d    14163  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31383.051746] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31383.051749] 47336 c801      0 8c478d70 cebaa9a6    13563  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31383.051775] 47337 c801      0 8c478d70 f7145d4d    13563  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31385.053182] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31385.053185] 47342 c801      0 8c478d70 f7145d4d    17980  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31387.054422] -pid- flgs status -client- --rqstp- -timeout ---ops--
[31387.054426] 47818 c801      0 8c478d70 f7145d4d    17761  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending
[31387.054467] 47819 c801      0 8c478d70 cebaa9a6    17762  8531859
nfsv4 READ a:call_status [sunrpc] q:xprt_pending


- mike


On Sun, Aug 8, 2021 at 5:28 PM Mike Javorski <mike.javorski@gmail.com> wrote:
>
> Appreciate the insights Neil. I will make an attempt to
> trigger/capture the fault if I can.
>
> - mike
>
> On Sun, Aug 8, 2021 at 5:01 PM NeilBrown <neilb@suse.de> wrote:
> >
> > On Mon, 09 Aug 2021, Mike Javorski wrote:
> > > I have been experiencing nfs file access hangs with multiple release
> > > versions of the 5.13.x linux kernel. In each case, all file transfers
> > > freeze for 5-10 seconds and then resume. This seems worse when reading
> > > through many files sequentially.
> >
> > A particularly useful debugging tool for NFS freezes is to run
> >
> >   rpcdebug -m rpc -c all
> >
> > while the system appears frozen.  As you only have a 5-10 second window
> > this might be tricky.
> > Setting or clearing debug flags in the rpc module (whether they are
> > already set or not) has a side effect if listing all RPC "tasks" which a
> > waiting for a reply.  Seeing that task list can often be useful.
> >
> > The task list appears in "dmesg" output.  If there are not tasks
> > waiting, nothing will be written which might lead you to think it didn't
> > work.
> >
> > As Chuck hinted, tcpdump is invaluable for this sort of problem.
> >   tcpdump -s 0 -w /tmp/somefile.pcap port 2049
> >
> > will capture NFS traffic.  If this can start before a hang, and finish
> > after, it may contain useful information.  Doing that in a way that
> > doesn't create an enormous file might be a challenge.  It would help if
> > you found a way trigger the problem.  Take note of the circumstances
> > when it seems to happen the most.  If you can only produce a large file,
> > we can probably still work with it.
> >   tshark -r /tmp/somefile.pcap
> > will report the capture one line per packet.  You can look for the
> > appropriate timestamp, note the frame numbers, and use "editcap"
> > to extract a suitable range of packets.
> >
> > NeilBrown
> >
> >
> > >
> > > My server:
> > > - Archlinux w/ a distribution provided kernel package
> > > - filesystems exported with "rw,sync,no_subtree_check,insecure" options
> > >
> > > Client:
> > > - Archlinux w/ latest distribution provided kernel (5.13.9-arch1-1 at writing)
> > > - nfs mounted via /net autofs with "soft,nodev,nosuid" options
> > > (ver=4.2 is indicated in mount)
> > >
> > > I have tried the 5.13.x kernel several times since the first arch
> > > release (most recently with 5.13.9-arch1-1), all with similar results.
> > > Each time, I am forced to downgrade the linux package to a 5.12.x
> > > kernel (5.12.15-arch1 as of writing) to clear up the transfer issues
> > > and stabilize performance. No other changes are made between tests. I
> > > have confirmed the freezing behavior using both ext4 and btrfs
> > > filesystems exported from this server.
> > >
> > > At this point I would appreciate some guidance in what to provide in
> > > order to diagnose and resolve this issue. I don't have a lot of kernel
> > > debugging experience, so instruction would be helpful.
> > >
> > > - mike
> > >
> > >