Bug 150209

Description of problem:
When running autofs and accessing/expiring mount points repeatedly, the system
will slowly leak kernel memory.  On my 128MB celeron, an over-night run of the
below test caused the system load average to hit 5, and the system to be pretty
unusable.  The size-256 slab looks like so:

size-256          365535 365535    256 24369 24369    1 :  252   63

Note that the system only has 128MB of ram, and this is taking roughly 90MB!

Version-Release number of selected component (if applicable):
2.4.21-28.ELsmp

How reproducible:
I'm not sure yet, but it is a very controlled test case, so I will know soon.

Steps to Reproduce:
1. Setup a server to export /export/<dir>
2. Create a number of directories under /export/<dir> like so:
   for n in `seq 1 48`; do mkdir $n; touch $n/$n; done
3. Now, on the client, create an automounter map to point at your server:
   (replace <IP> with the server IP)
   for n in `seq 1 48`; do echo "$n <IP>:/export/<dir>/$n" >> /etc/auto.test ; done
4. Create an entry in the auto.master on the client to point at this map:
   echo "/test /etc/auto.test --timeout=1" >> /etc/auto.master
5. Restart autofs on the client.
6. ensure that nfs services are running on the server
7. On the client, create a script that does this:
   while true; do for n in `seq 1 48`; do ls  /test/$n ; done; sleep 2; done
8. For my test, I ran two copies of this script on the client.
Actual results:
The kernel will slowly leak memory, and the system will begin to swap.  The load
average will climb, as well.

Expected results:
The kernel should not leak memory!

Additional info:
I'm in the process of trying to reproduce this without autofs in the picture.  I
get messages like this in the kernel log:

nfs_get_root: getattr error = 5
nfs_read_super: get root inode failed
nfs warning: mount version older than kernel
RPC: Can't bind to reserved port (98).

So the error cases for nfs are suspect.  If I can't reproduce this without
autofs, then I'll try to reproduce without nfs.  This can be achieved by making
the client also the server.  The client automount map would then point to
localhost, and the automound daemon will do bind mounts instead of nfs mounts.