[QUESTION] about NFS sub system between Public Kernel and Red Hat Kernel.

[QUESTION] about NFS sub system between Public Kernel and Red Hat Kernel.

[gchen]

Hi linux-nfs@vger.kernel.org

I have 1 question, and also 2 conclusions which need confirm.


1) Question:

Jeff Layton said in Red Hat Bugzilla (bug 848706):
"Have configuration where the same host is acting as both NFS client
and server. That's a configuration known to cause deadlocks."

Does it mean that the public Linux kernel (not Red Hat) also can cause
deadlocks if NFS client and server are under the same machine ?


2) Confirm 1: (better by Jeff Layton)

For function nfs_commit_set_lock in ./fs/nfs/write.c

for latest public kernel version:
the parameters of out_of_line_wait_on_bit_lock() are
(&nfsi->flags, NFS_INO_COMMIT, nfs_wait_killable, TASK_KILLABLE)
for Red Hat kernel version: kernel-2.6.18-308.4.1.el5
the parameters of out_of_line_wait_on_bit_lock() are
(&nfsi->flags, NFS_INO_COMMIT,
nfs_wait_bit_uninterruptible, TASK_UNINTERRUPTIBLE)

It means for red hat version:
when deadlock occurs, we can not boot machine in normal way
(it is true for my test machine, the deadlock task can not be killed)
It means for public kernel version:
"Assume deadlock occurs", we can still boot machine in normal way,
because the task can be killed.

Is what I said above correct ?


3) Confirm 2:

Is LTP (Linux Test Project) still a suitable test tools for public kernel ?
(for ltp-full-20100331.gz stress test, it mounts NFS on local machine,
and the latest LTP ltp-full-20120401.bz2 also seems the same).



thanks.

gchen

Asianux Corporation

Re: [QUESTION] about NFS sub system between Public Kernel and Red Hat Kernel.

[Jeff Layton]

On Fri, 31 Aug 2012 13:40:16 +0800
gchen <gang.chen@asianux.com> wrote:

> Hi linux-nfs@vger.kernel.org
> 
> I have 1 question, and also 2 conclusions which need confirm.
> 
> 
> 1) Question:
> 
> Jeff Layton said in Red Hat Bugzilla (bug 848706):
> "Have configuration where the same host is acting as both NFS client
> and server. That's a configuration known to cause deadlocks."
> 
> Does it mean that the public Linux kernel (not Red Hat) also can cause
> deadlocks if NFS client and server are under the same machine ?
> 

Yes.

> 
> 2) Confirm 1: (better by Jeff Layton)
> 
> For function nfs_commit_set_lock in ./fs/nfs/write.c
> 
> for latest public kernel version:
> the parameters of out_of_line_wait_on_bit_lock() are
> (&nfsi->flags, NFS_INO_COMMIT, nfs_wait_killable, TASK_KILLABLE)
> for Red Hat kernel version: kernel-2.6.18-308.4.1.el5
> the parameters of out_of_line_wait_on_bit_lock() are
> (&nfsi->flags, NFS_INO_COMMIT,
> nfs_wait_bit_uninterruptible, TASK_UNINTERRUPTIBLE)
> 
> It means for red hat version:
> when deadlock occurs, we can not boot machine in normal way
> (it is true for my test machine, the deadlock task can not be killed)
> It means for public kernel version:
> "Assume deadlock occurs", we can still boot machine in normal way,
> because the task can be killed.
> 
> Is what I said above correct ?
> 

Not sure I understand your question. RHEL5 doesn't have support for
TASK_KILLABLE, and I didn't backport it, hence the difference in that
function.

> 
> 3) Confirm 2:
> 
> Is LTP (Linux Test Project) still a suitable test tools for public kernel ?
> (for ltp-full-20100331.gz stress test, it mounts NFS on local machine,
> and the latest LTP ltp-full-20120401.bz2 also seems the same).
> 

That I'm not sure of. All I can tell you is that mounts over loopback
(or similar configurations) are easily deadlockable under load.

-- 
Jeff Layton <jlayton@redhat.com>

Re: [QUESTION] about NFS sub system between Public Kernel and Red Hat Kernel.

[gchen]

于 2012年08月31日 22:02, Jeff Layton 写道:
> On Fri, 31 Aug 2012 13:40:16 +0800
> gchen <gang.chen@asianux.com> wrote:
>
>> Hi linux-nfs@vger.kernel.org
>>
>> I have 1 question, and also 2 conclusions which need confirm.
>>
>>
>> 1) Question:
>>
>> Jeff Layton said in Red Hat Bugzilla (bug 848706):
>> "Have configuration where the same host is acting as both NFS client
>> and server. That's a configuration known to cause deadlocks."
>>
>> Does it mean that the public Linux kernel (not Red Hat) also can cause
>> deadlocks if NFS client and server are under the same machine ?
>>
> Yes.

I will communicate with LTP (Linux Test Project) to confirm it, too.

And, it will be better if other members in linux-nfs@vger.kernel.org
also confirm it.

>> 2) Confirm 1: (better by Jeff Layton)
>>
>> For function nfs_commit_set_lock in ./fs/nfs/write.c
>>
>> for latest public kernel version:
>> the parameters of out_of_line_wait_on_bit_lock() are
>> (&nfsi->flags, NFS_INO_COMMIT, nfs_wait_killable, TASK_KILLABLE)
>> for Red Hat kernel version: kernel-2.6.18-308.4.1.el5
>> the parameters of out_of_line_wait_on_bit_lock() are
>> (&nfsi->flags, NFS_INO_COMMIT,
>> nfs_wait_bit_uninterruptible, TASK_UNINTERRUPTIBLE)
>>
>> It means for red hat version:
>> when deadlock occurs, we can not boot machine in normal way
>> (it is true for my test machine, the deadlock task can not be killed)
>> It means for public kernel version:
>> "Assume deadlock occurs", we can still boot machine in normal way,
>> because the task can be killed.
>>
>> Is what I said above correct ?
>>
> Not sure I understand your question. RHEL5 doesn't have support for
> TASK_KILLABLE, and I didn't backport it, hence the difference in that
> function.

I agree with what you said above.

Thanks for your confirmation.

>> 3) Confirm 2:
>>
>> Is LTP (Linux Test Project) still a suitable test tools for public kernel ?
>> (for ltp-full-20100331.gz stress test, it mounts NFS on local machine,
>> and the latest LTP ltp-full-20120401.bz2 also seems the same).
>>
> That I'm not sure of. All I can tell you is that mounts over loopback
> (or similar configurations) are easily deadlockable under load.
>

I will communicate with LTP (Linux Test Project) about these informations.


Thanks.

gchen.

Asianux Corporation.