NFS mounts being mounted read-only depending upon mount order???

[Michael Walker <Michael.Walker@Cassatt.COM>]

All,

I'm having problems with the latest version of FC5 which
contains kernel 2.6.18 - the problem is that NFS mounts
of read-write file-systems are being mounted read-only, sometimes.

Whether a mount is mounted read-only or read-write seems
to very depending upon what other directories were
mounted from the same server and with what options.

Take the following file-systems exported from my
Linux Server server:

    root@polyslo:/proc/fs/nfs# cat /etc/exports
    /disk1/dir_ro   *(ro,no_root_squash,sync,wdelay,no_subtree_check)
    /disk1/dir_rw   *(rw,no_root_squash,sync,wdelay,no_subtree_check)
    root@polyslo:/proc/fs/nfs# showmount -e 10.20.20.48
    Export list for 10.20.20.48:
    /disk1/dir_rw *
    /disk1/dir_ro *
    root@polyslo:/proc/fs/nfs#

If I now do the following mounts (in this order):

    # Mount initial directory read-only - this is intentional
    mount -t nfs -o ro 10.20.20.48:/disk1/dir_ro /tmp/dir_ro

    # Attempt to mount second directory read-write
    mount -t nfs -o rw 10.20.20.48:/disk1/dir_rw /tmp/dir_rw

    # Now I attempt to touch a file in the rw directory:
    [root@vt-1 tmp]# touch /tmp/dir_rw/hello
    touch: cannot touch `/tmp/dir_rw/hello': Read-only file system

    # And if I take a look in the /proc/mounts directory - I see
    # that the directory was truly mounted read-only

    [root@vt-1 tmp]# grep 10.20.20.48 /proc/mounts
    10.20.20.48:/disk1/dir_ro /tmp/dir_ro nfs ro,vers=3,rsize=32768,wsize=32768,hard,proto=tcp,timeo=600,retrans=2,sec=sys,addr=10.20.20.48 0 0
    10.20.20.48:/disk1/dir_rw /tmp/dir_rw nfs ro,vers=3,rsize=32768,wsize=32768,hard,proto=tcp,timeo=600,retrans=2,sec=sys,addr=10.20.20.48 0 0
    [root@vt-1 tmp]#

The above seems wrong to me - can someone clarify what's going on.
I know that this is new behavior that was not true in the past.  My
RHEL_4U4 server running 2.6.9 kernel does not have this problem.

Notice that if I change the order of the mounts I get different behavior:

    # Initially mount the read-write directory:
    mount -t nfs -o rw 10.20.20.48:/disk1/dir_rw /tmp/dir_rw

    # Then mount the read-only directory:
    mount -t nfs -o ro 10.20.20.48:/disk1/dir_ro /tmp/dir_ro

    # Now the directories are mounted as I wish, I can write to the
    # read-write mount:
    [root@vt-1 tmp]# touch /tmp/dir_rw/hello
    [root@vt-1 tmp]#

    # And the read-only directory is read-only:
    [root@vt-1 tmp]# touch /tmp/dir_ro/hello
    touch: cannot touch `/tmp/dir_ro/hello': Read-only file system
    [root@vt-1 tmp]#

    # And the /proc/mounts file reflects the states I expect
    [root@vt-1 tmp]# grep 10.20.20.48 /proc/mounts
    10.20.20.48:/disk1/dir_rw /tmp/dir_rw nfs rw,vers=3,rsize=32768,wsize=32768,hard,proto=tcp,timeo=600,retrans=2,sec=sys,addr=10.20.20.48 0 0
    10.20.20.48:/disk1/dir_ro /tmp/dir_ro nfs rw,vers=3,rsize=32768,wsize=32768,hard,proto=tcp,timeo=600,retrans=2,sec=sys,addr=10.20.20.48 0 0
    [root@vt-1 tmp]#


Note that previously the order did not matter and the permissions
always reflected the permissions of the individual mount requests.

If someone could provide insights on what's going on above that
would be great.  This is a artificial test case - but it's actually
hitting code we have in production and will be a significant
issue for us.

Thanx much!

_Mike_

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