Re: Random IO errors on nfs clients running linux > 4.20

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Oct 26, 2020 at 02:42:16PM +0100, Alberto Gonzalez Iniesta wrote:
> On Wed, Sep 09, 2020 at 09:47:27AM -0400, J. Bruce Fields wrote:
> > On Wed, Sep 09, 2020 at 11:29:00AM +0200, Alberto Gonzalez Iniesta wrote:
> > > On Thu, Apr 30, 2020 at 01:32:00PM -0400, J. Bruce Fields wrote:
> > > > On Wed, Apr 29, 2020 at 07:15:27PM +0200, Alberto Gonzalez Iniesta wrote:
> > > > > We can run the previous "ls -lR" 20 times and get no error, or get
> > > > > this "ls: leyendo el directorio 'Becas y ayudas/': Error de entrada/salida"
> > > > > (ls: reading directorio 'Becas y ayudas/': Input/Output Error") every
> > > > > now and then.
> > > > > 
> > > > > The error happens (obviously?) with ls, rsync and the users's GUI tools.
> > > > > 
> > > > > There's nothing in dmesg (or elsewhere).
> > > > > These are the kernels with tried:
> > > > > 4.18.0-25   -> Can't reproduce
> > > > > 4.19.0      -> Can't reproduce
> > > > > 4.20.17     -> Happening (hard to reproduce)
> > > > > 5.0.0-15    -> Happening (hard to reproduce)
> > > > > 5.3.0-45    -> Happening (more frequently)
> > > > > 5.6.0-rc7   -> Reproduced a couple of times after boot, then nothing
> > > > > 
> > > > > We did long (as in daylong) testing trying to reproduce this with all
> > > > > those kernel versions, so we are pretty sure 4.18 and 4.19 don't
> > > > > experience this and our Ubuntu 16.04 clients don't have any issue.
> > > > > 
> > > > > I know we aren't providing much info but we are really looking forward
> > > > > to doing all the testing required (we already spent lots of time in it).
> > > > > 
> > > > > Thanks for your work.
> > 
> > So all I notice from this one is the readdir EIO came from call_decode.
> > I suspect that means it failed in the xdr decoding.  Looks like xdr
> > decoding of the actual directory data (which is the complicated part) is
> > done later, so this means it failed decoding the header or verifier,
> > which is a little odd:
> > 
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016276] RPC:  3284 call_decode result -5
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016281] nfs41_sequence_process: Error 1 free the slot 
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016286] RPC:       wake_up_first(00000000d3f50f4d "ForeChannel Slot table")
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016288] nfs4_free_slot: slotid 0 highest_used_slotid 4294967295
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016290] RPC:  3284 return 0, status -5
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016291] RPC:  3284 release task
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016295] RPC:       freeing buffer of size 4144 at 00000000a3649daf
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016298] RPC:  3284 release request 0000000079df89b2
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016300] RPC:       wake_up_first(00000000c5ee49ee "xprt_backlog")
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016302] RPC:       rpc_release_client(00000000b930c343)
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016304] RPC:  3284 freeing task
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016309] _nfs4_proc_readdir: returns -5
> > > Sep  8 16:03:23 portatil264 kernel: [15033.016318] NFS: readdir(departamentos/innovacion) returns -5
> 
> Hi, Bruce et al.
> 
> Is there anything we can do to help debugging/fixing this? It's still
> biting our users with a +4.20.x kernel.

Sorry, I just don't know what this is off the top of my head.  If I had
the time, stuff I might try:

	- look at the wire traffic with wireshark: try to figure out
	  which operation this is happening on, and if there's anything
	  unusual about the reply.  May be difficult if a lot of traffic
	  is required to reproduce.
	- if you're using krb5, try without just to see if that makes a
	  difference.
	- look at history: gitk v4.19..v4.20.17 fs/nfs net/sunrpc, see
	  if anything looks relevant; or even just try a git bisect
	  (difficult again given the intermittent failure).
	- trace through the code to work out where call_decode might be
	  returning -EIO, try to narrow it down with tracepoints or even
	  just debugging printk's.

--b.