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Date: Fri, 22 Mar 2013 07:40:03 -0400
From: Jeff Layton <jlayton@redhat.com>
To: ycnian@gmail.com
Cc: Trond.Myklebust@netapp.com, linux-nfs@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: nfsv4.1 client refuses to suspend
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On Fri, 22 Mar 2013 10:57:21 +0800
ycnian@gmail.com wrote:

> nfsv4.1 client suspending fails with such info
> 
> Freezing of tasks failed after 20.00 seconds (1 tasks refusing to freeze, wq_busy=0):
> nfsv4.1-svc     S ffff88007889f2e0     0  3191      2 0x00000080   
>  ffff88007b2f3e28 0000000000000046 ffff88007b2f2010 00000000000127c0
>  ffff880079b08000 00000000000127c0 ffff88007b2f3fd8 00000000000127c0
>  ffff88007b2f3fd8 00000000000127c0 ffffffff81a14410 ffff880079b08000
> Call Trace:
>  [<ffffffff81441396>] schedule+0x64/0x66
>  [<ffffffffa06a6892>] nfs41_callback_svc+0x100/0x129 [nfsv4]
>  [<ffffffff8104fdb8>] ? wake_up_bit+0x2a/0x2a
>  [<ffffffffa06a6792>] ? nfs_callback_up+0x548/0x548 [nfsv4]
>  [<ffffffff8104f7e0>] kthread+0xb5/0xbd
>  [<ffffffff8104f72b>] ? kthread_freezable_should_stop+0x65/0x65
>  [<ffffffff8144912c>] ret_from_fork+0x7c/0xb0
>  [<ffffffff8104f72b>] ? kthread_freezable_should_stop+0x65/0x65
> 
> I read such threads
> [1] nfs/sunrpc: allow freezing of tasks with NFS calls in flight
> [2] LOCKDEP: 3.9-rc1: mount.nfs/4272 still has locks held!
> and then modify nfs41_callback_svc(). It works on my machine. I don't know
> the details of freezing, so I'm not sure if the modification is reasonable.
> This is not a formal patch. Thanks.
> 
> Signed-off-by: Yanchuan Nian <ycnian@gmail.com>
> ---
>  fs/nfs/callback.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
> index 5088b57..8addb7b 100644
> --- a/fs/nfs/callback.c
> +++ b/fs/nfs/callback.c
> @@ -138,7 +138,7 @@ nfs41_callback_svc(void *vrqstp)
>  				error);
>  		} else {
>  			spin_unlock_bh(&serv->sv_cb_lock);
> -			schedule();
> +			freezable_schedule();
>  		}
>  		finish_wait(&serv->sv_cb_waitq, &wq);
>  	}

I think it'd be better to have that thread call try_to_freeze()
directly instead of doing this. There are some problems with
freezable_schedule() that still need to be resolved and I suspect that
it will eventually go away entirely.

It's may be sufficient to simply call try_to_freeze() at the top of
the loop, but that would need to be tested.

-- 
Jeff Layton <jlayton@redhat.com>