Re: [PATCH 0/6] Fix up NFS client mount option regressions

[Trond Myklebust <trondmy@kernel.org>]

On Fri, 2026-01-30 at 09:34 +0800, Li Lingfeng wrote:
> Hi Trond,
> 
> 在 2026/1/30 0:00, Trond Myklebust 写道:
> > On Thu, 2026-01-29 at 15:06 +0800, Li Lingfeng wrote:
> > > Hi Trond,
> > > 
> > > 在 2025/11/29 12:06, Trond Myklebust 写道:
> > > > From: Trond Myklebust <trond.myklebust@hammerspace.com>
> > > > 
> > > > The recent changes to suppress the 'ro' and 'rw' mount options
> > > > when
> > > > mounting the same NFS filesystem with different settings are
> > > > causing
> > > > confusion with users, and are an unnecessary restriction. They
> > > > represent
> > > > a functionality regression.
> > > > 
> > > > The following patch set reverts the regressions, before
> > > > applying a
> > > > different set of fixes to address the original problem, which
> > > > was
> > > > one of
> > > > the NFSv4 mount automounter code failing to propagate the
> > > > correct
> > > > mount
> > > > options.
> > > > 
> > > > Trond Myklebust (6):
> > > >     Revert "nfs: ignore SB_RDONLY when remounting nfs"
> > > >     Revert "nfs: clear SB_RDONLY before getting superblock"
> > > >     Revert "nfs: ignore SB_RDONLY when mounting nfs"
> > > >     NFS: Automounted filesystem should inherit
> > > > ro,noexec,nodev,sync
> > > > flags
> > > >     NFS: Fix inheritance of the block sizes when automounting
> > > >     NFS: Fix up the automount fs_context to use the correct
> > > > cred
> > > > 
> > > >    fs/nfs/client.c           | 21 +++++++++++++++++----
> > > >    fs/nfs/internal.h         |  3 +--
> > > >    fs/nfs/namespace.c        | 16 +++++++++++++++-
> > > >    fs/nfs/nfs4client.c       | 18 ++++++++++++++----
> > > >    fs/nfs/super.c            | 33 +++--------------------------
> > > > ----
> > > >    include/linux/nfs_fs_sb.h |  5 +++++
> > > >    6 files changed, 55 insertions(+), 41 deletions(-)
> > > After this series of patches was merged, I found that the issue
> > > described
> > > in link [1] has appeared again.
> > > 
> > > [root@nfs-client1 ~]# mount /dev/sda /mnt2
> > > [root@nfs-client1 ~]# echo "/mnt2 *(rw,no_root_squash,fsid=0)"
> > > > /etc/exports
> > > [root@nfs-client1 ~]# systemctl restart nfs-server
> > > [root@nfs-client1 ~]# mount -t nfs -o ro,vers=4 127.0.0.1:/
> > > /mnt/sdaa
> > > [root@nfs-client1 ~]# mount -t nfs -o rw,vers=4 127.0.0.1:/
> > > /mnt/sdaa
> > > [root@nfs-client1 ~]# mount -t nfs -o ro,vers=4 127.0.0.1:/
> > > /mnt/sdaa
> > > [root@nfs-client1 ~]# mount -t nfs -o rw,vers=4 127.0.0.1:/
> > > /mnt/sdaa
> > > [root@nfs-client1 ~]# mount | grep nfs4
> > > 127.0.0.1:/ on /mnt/sdaa type nfs4
> > > (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard
> > > ,fat
> > > al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientadd
> > > r=12
> > > 7.0.0.1,local_lock=none,addr=127.0.0.1)
> > > 127.0.0.1:/ on /mnt/sdaa type nfs4
> > > (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard
> > > ,fat
> > > al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientadd
> > > r=12
> > > 7.0.0.1,local_lock=none,addr=127.0.0.1)
> > > 127.0.0.1:/ on /mnt/sdaa type nfs4
> > > (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard
> > > ,fat
> > > al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientadd
> > > r=12
> > > 7.0.0.1,local_lock=none,addr=127.0.0.1)
> > > 127.0.0.1:/ on /mnt/sdaa type nfs4
> > > (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard
> > > ,fat
> > > al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientadd
> > > r=12
> > > 7.0.0.1,local_lock=none,addr=127.0.0.1)
> > > [root@nfs-client1 ~]# uname -a
> > > Linux nfs-client1 6.19.0-rc7+ #178 SMP PREEMPT_DYNAMIC Thu Jan 29
> > > 14:06:54 CST 2026 x86_64 x86_64 x86_64 GNU/Linux
> > > [root@nfs-client1 ~]#
> > > 
> > > [1]
> > > https://lore.kernel.org/all/20241114045303.1656426-1-lilingfeng3@huawei.com/
> > > 
> > > Thanks,
> > > Lingfeng.
> > What does the output of "cat /proc/fs/nfsfs/volumes" show? Does it
> > show
> > more than 2 devices associated with that fsid?
> >   
> 
> Here is the result of the test:
> 
> [root@nfs-client1 ~]# mount /dev/sda /mnt2
> [root@nfs-client1 ~]# echo "/mnt2 *(rw,no_root_squash,fsid=0)"
> >/etc/exports
> [root@nfs-client1 ~]# systemctl restart nfs-server
> [root@nfs-client1 ~]# mount -t nfs -o ro,vers=4 127.0.0.1:/ /mnt/sdaa
> [root@nfs-client1 ~]# cat /proc/fs/nfsfs/volumes
> NV SERVER   PORT DEV          FSID FSC
> v4 7f000001  801 0:51         0:0                               no
> [root@nfs-client1 ~]# mount -t nfs -o rw,vers=4 127.0.0.1:/ /mnt/sdaa
> [root@nfs-client1 ~]# cat /proc/fs/nfsfs/volumes
> NV SERVER   PORT DEV          FSID FSC
> v4 7f000001  801 0:51         0:0                               no
> v4 7f000001  801 0:52         0:0                               no
> [root@nfs-client1 ~]# mount | grep nfs4
> 127.0.0.1:/ on /mnt/sdaa type nfs4 
> (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,fat
> al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=12
> 7.0.0.1)
> 127.0.0.1:/ on /mnt/sdaa type nfs4 
> (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,fat
> al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=12
> 7.0.0.1)
> [root@nfs-client1 ~]# mount -t nfs -o ro,vers=4 127.0.0.1:/ /mnt/sdaa
> [root@nfs-client1 ~]# mount -t nfs -o rw,vers=4 127.0.0.1:/ /mnt/sdaa
> [root@nfs-client1 ~]# cat /proc/fs/nfsfs/volumes
> NV SERVER   PORT DEV          FSID FSC
> v4 7f000001  801 0:51         0:0                               no
> v4 7f000001  801 0:52         0:0                               no
> [root@nfs-client1 ~]# mount | grep nfs4
> 127.0.0.1:/ on /mnt/sdaa type nfs4 
> (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,fat
> al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=12
> 7.0.0.1)
> 127.0.0.1:/ on /mnt/sdaa type nfs4 
> (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,fat
> al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=12
> 7.0.0.1)
> 127.0.0.1:/ on /mnt/sdaa type nfs4 
> (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,fat
> al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=12
> 7.0.0.1)
> 127.0.0.1:/ on /mnt/sdaa type nfs4 
> (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,fat
> al_neterrors=none,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=12
> 7.0.0.1)
> [root@nfs-client1 ~]#
> 
> There are only 2 devices associated with that fsid.
> 

Then it is working as expected. It's not the kernel's job to stop
people from stacking one mount on top of another. If it were, then the
right place to do that would be in the VFS and not the NFS client.

However the NFS client does try to ensure that mounts of the same
remote filesystem with the same set of mount options gets mapped to the
same super block (and hence device). The exception is if you're playing
with the nosharecache option; in that case you're knowingly asking the
kernel to ignore that constraint.

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