[LTP] [PATCH] lsmod01: parse a copy of /proc/modules

[Stanislav Kholmanskikh]

On 10/11/2016 04:38 PM, Cyril Hrubis wrote:
> Hi!
>> Tried this all again.
>>
>> This is from a 4.1-based kernel in a VirtualBox host:
>>
>> [root@ol6-x64 mnt]# mount|grep mnt
>> 127.0.0.1:/opt/ on /mnt type nfs (rw,vers=3,addr=127.0.0.1)
>> [root@ol6-x64 mnt]# grep sunrpc /proc/modules
>> sunrpc 329262 28
>> nfsv3,rpcsec_gss_krb5,nfsv4,nfs,nfsd,lockd,nfs_acl,auth_rpcgss, Live
>> 0xffffffffa0366000
>> [root@ol6-x64 mnt]# dd if=/dev/zero of=file bs=512
>>
>> While the above dd command is running, in a separate shell I see:
>>
>> [stas@ol6-x64 ~]$ lsmod|grep sunrpc
>> sunrpc                329262  36
>> nfsv3,rpcsec_gss_krb5,nfsv4,nfs,nfsd,lockd,nfs_acl,auth_rpcgss
>> [stas@ol6-x64 ~]$
> 
> Hmm, 36, really increased by 8 because of the one dd?
> 
> That sounds even more strange.
> 
>> [root@ol6-x64 mnt]# grep sunrpc /proc/modules
>> sunrpc 329262 28
>> nfsv3,rpcsec_gss_krb5,nfsv4,nfs,nfsd,lockd,nfs_acl,auth_rpcgss, Live
>> 0xffffffffa0366000
>> [root@ol6-x64 mnt]# dd if=/proc/modules bs=1 | cat > temp2; grep sunrpc
>> temp2
>> 2564+0 records in
>> 2564+0 records out
>> 2564 bytes (2.6 kB) copied, 0.00313203 s, 819 kB/s
>> sunrpc 329262 29
>> nfsv3,rpcsec_gss_krb5,nfsv4,nfs,nfsd,lockd,nfs_acl,auth_rpcgss, Live
>> 0xffffffffa0366000
>> [root@ol6-x64 mnt]#
>>
>> The same situation is with NFSv4.
>>
>> So it turns out that writing to a file on NFS increases the sunrpc
>> module reference counter. I don't observe this with ext4.ko.
>>
>> So I find that my original patch is fine, it just needs a proper
>> description.
>>
>> Thoughts?
> 
> Isn't the original patch just workaround? Since we write to the nfs
> TMPDIR as well, just differently, there is always possibility that we
> only made the problem less probable and that it will fail in one of
> thousand runs. Have you tried to run the test in a loop for some time?

Yes, the original patch is a workaround.

On my system I met 1 failure of 20000 runs (~1 hour).

Maybe we need to follow your proposal and test only the first two fields
from lsmod.


>