umount error: device is busy after nfs + lock

[wang dengyi <dy_wang@yahoo.com>]

Hello,

When I ran ltp test case:tlocklfs, I met a old problem
with the kernel:2.6.9. I can not umount a file system
after nfs and lock using it. Here is the steps.
 1) mount /dev/sda3 /xyz
 2) export /xyz
 3) restart nfs
 4) mount 127.0.0.1:/xyz /mnt/nfs_xyz
 5) run the special lock test program: "tlocklfs -t 7
/mnt/nfs_xyz
 6) umount /mnt/nfs_xyz
 7) stop nfs
 8) umount /xyz
Then I got the error: "umount /xyz: device is busy".
And the error displays twice. 

If I run the different lock test case for the step 5,
the umount works fine. It only failed on the test case
7 from tlocklfs. 

There are 2 processes in this special test case.
First, the parent process "setlk" for a file from nfs
file system. Then the child process "setlkw". At the
end, the parent and the child process unlock the file.


With some debug line in the code, I found the file
system's "mnt_count" is 3 instead of 2 before
umounting it. I traced back the problem and I'm lost
in linux/net/sunrpc/sched.c. Could anyone give me some
hint? Thank you very much.

Best regard

Dengyi Wang
  

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