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From:   Michael Wakabayashi <mwakabayashi@vmware.com>
To:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: NFSv4: Mounting NFS server which is down, blocks all other NFS mounts
 on same machine
Thread-Topic: NFSv4: Mounting NFS server which is down, blocks all other NFS
 mounts on same machine
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Date:   Mon, 17 May 2021 01:37:33 +0000
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Hi,=0A=
=0A=
We're seeing what looks like an NFSv4 issue.=0A=
=0A=
Mounting an NFS server that is down (ping to this NFS server's IP address d=
oes not respond) will block _all_ other NFS mount attempts even if the NFS =
servers are available and working properly (these subsequent mounts hang).=
=0A=
=0A=
If I kill the NFS mount process that's trying to mount the dead NFS server,=
 the NFS mounts that were blocked will immediately unblock and mount succes=
sfully, which suggests the first mount command is blocking the other mount =
commands.=0A=
=0A=
=0A=
I verified this behavior using a newly built mount.nfs command from the rec=
ent nfs-utils 2.5.3 package installed on a recent version of Ubuntu Cloud I=
mage 21.04:=0A=
* https://sourceforge.net/projects/nfs/files/nfs-utils/2.5.3/=0A=
* https://cloud-images.ubuntu.com/releases/hirsute/release-20210513/ubuntu-=
21.04-server-cloudimg-amd64.ova=0A=
=0A=
=0A=
The reason this looks like it is specific to NFSv4 is from the following ou=
tput showing "vers=3D4.2":=0A=
> $ strace /sbin/mount.nfs <unreachable-IP-address>:/path /tmp/mnt=0A=
> [ ... cut ... ]=0A=
> mount("<unreadhable-IP-address>:/path", "/tmp/mnt", "nfs", 0, "vers=3D4.2=
,addr=3D<unreachable-IP-address>,clien"...^C^Z=0A=
=0A=
Also, if I try the same mount.nfs commands but specifying NFSv3, the mount =
to the dead NFS server hangs, but the mounts to the operational NFS servers=
 do not block and mount successfully; this bug doesn't happen when using NF=
Sv3.=0A=
=0A=
=0A=
We reported this issue under util-linux here:=0A=
https://github.com/karelzak/util-linux/issues/1309=0A=
[mounting nfs server which is down blocks all other nfs mounts on same mach=
ine #1309]=0A=
=0A=
I also found an older bug on this mailing list that had similar symptoms (b=
ut could not tell if it was the same problem or not):=0A=
https://patchwork.kernel.org/project/linux-nfs/patch/87vaori26c.fsf@notaben=
e.neil.brown.name/=0A=
[[PATCH/RFC] NFSv4: don't let hanging mounts block other mounts]=0A=
=0A=
Thanks, Mike=