Re: nfs4 server stops responding

[Trond Myklebust <trondmy@hammerspace.com>]

On Mon, 2019-08-19 at 12:25 +0000, Rantala, Tommi T. (Nokia - FI/Espoo)
wrote:
> Hello,
> 
> I have two VMs, exporting some directories in one VM:
> # cat /etc/exports
> /mnt 192.168.1.0/24(ro,fsid=0,no_subtree_check,sync)
> /mnt/export
> 192.168.1.0/24(rw,no_root_squash,sync,no_wdelay,no_subtree_check)
> [...]

Are /mnt and /mnt/export on different filesystems? If not, then your
server configuration is pretty much guaranteed to be broken, with
conflicting sets of rules being imposed on /mnt/export. I'm guessing
that is the case, because I'm not seeing any 'nohide' or 'crossmnt'
entries above.

> 
> And NFS mounting in the second VM:
> # grep nfs /proc/mounts 
> server:/export /mnt/export nfs4
> rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,
> acregmin=1,acregmax=1,acdirmin=1,acdirmax=1,hard,nordirplus,
> proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.1.11,
> local_lock=none,addr=192.168.1.10 0 0
> [...]
> 
> If I keep some file descriptor open for several minutes in the second
> VM,
> for example by running this:
> # sleep 10m >/mnt/export/test
> 
> Then result is that the NFS mount stops responding: the sleep process
> never finished but is "forever" stuck in (killable) D state, and any
> I/O
> attempt from other processes in /mnt/export never finish.
> It's always reproducible with this sleep command.
> To recover the mountpoint I need to reboot the second VM.
> 
> Kernel version is 5.3.0-rc4 in both VMs.
> Also reproducible with 4.14.x and 4.19.x
> 
> # ps aux|grep sleep
> root      2524  0.0  0.0   5900   688 pts/0    D    14:04   0:00
> sleep 5m
> 
> # grep -C100 nfs /proc/*/stack
> /proc/2524/stack:[<0>] nfs4_do_close+0x87d/0xb20 [nfsv4]
> /proc/2524/stack:[<0>] __put_nfs_open_context+0x297/0x4f0 [nfs]
> /proc/2524/stack:[<0>] nfs_file_release+0xbe/0xf0 [nfs]
> /proc/2524/stack-[<0>] __fput+0x1df/0x690
> /proc/2524/stack-[<0>] task_work_run+0x123/0x1b0
> /proc/2524/stack-[<0>] exit_to_usermode_loop+0x121/0x140
> /proc/2524/stack-[<0>] do_syscall_64+0x2d1/0x370
> /proc/2524/stack-[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> --
> /proc/561/stack-[<0>] __rpc_execute+0x692/0xb10 [sunrpc]
> /proc/561/stack-[<0>] rpc_run_task+0x45f/0x5d0 [sunrpc]
> /proc/561/stack:[<0>] nfs4_call_sync_sequence+0x12a/0x210 [nfsv4]
> /proc/561/stack:[<0>] _nfs4_proc_getattr+0x19a/0x200 [nfsv4]
> /proc/561/stack:[<0>] nfs4_proc_getattr+0xda/0x230 [nfsv4]
> /proc/561/stack:[<0>] __nfs_revalidate_inode+0x2ed/0x7a0 [nfs]
> /proc/561/stack:[<0>] nfs_do_access+0x605/0xd00 [nfs]
> /proc/561/stack:[<0>] nfs_permission+0x500/0x5e0 [nfs]
> /proc/561/stack-[<0>] inode_permission+0x2dd/0x3f0
> /proc/561/stack-[<0>] link_path_walk.part.60+0x681/0xe40
> /proc/561/stack-[<0>] path_lookupat.isra.63+0x1af/0x850
> /proc/561/stack-[<0>] filename_lookup.part.79+0x165/0x360
> /proc/561/stack-[<0>] vfs_statx+0xb9/0x140
> /proc/561/stack-[<0>] __do_sys_newstat+0x77/0xd0
> /proc/561/stack-[<0>] do_syscall_64+0x9a/0x370
> /proc/561/stack-[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> 
> In dmesg of second VM sometimes nfs complaints are seen:
> 
> [  386.362897] nfs: server xyz not responding, still trying
> 
> Any ideas what's going wrong here...?
> 
The 'server not responding' implies that there is a network connection
issue. Does 'netstat -nt | grep :2049' show a correctly established TCP
connection between the client and server VMs?

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com