Re: [PATCH 1/1] NFSv4.1 fix a kswap nfs4_state_manger race

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On Nov 25, 2013, at 13:13, Myklebust, Trond <Trond.Myklebust@xxxxxxxxxx> wrote:

> 
> On Nov 25, 2013, at 12:57, <andros@xxxxxxxxxx> <andros@xxxxxxxxxx> wrote:
> 
>> From: Andy Adamson <andros@xxxxxxxxxx>
>> 
>> The state manager is recovering expired state and recovery OPENs are being
>> processed. If kswapd is pruning inodes at the same time, a deadlock can occur
>> when kswapd calls evict_inode on an NFSv4.1 inode with a layout, and the
>> resultant layoutreturn gets an error that the state mangager is to handle,
>> causing the layoutreturn to wait on the (NFS client) cl_rpcwaitq.
>> 
>> At the same time an open is waiting for the inode deletion to complete in
>> __wait_on_freeing_inode.
>> 
>> If the open is either the open called by the state manager, or an open from
>> the same open owner that is holding the NFSv4.0 sequence id which causes the
>> OPEN from the state manager to wait for the sequence id on the Seqid_waitqueue,
>> then the state is deadlocked with kswapd.
>> 
>> Do not handle LAYOUTRETURN errors when called from nfs4_evict_inode.
> 
> Why are we waiting for recovery in LAYOUTRETURN at all? Layouts are automatically lost when the server reboots or when the lease is otherwise lost.
> 
> IOW: Is there any reason why we need to special-case nfs4_evict_inode? Shouldn’t we just bail out on error in _all_ cases?

BTW: Is it possible that we might have a similar problem with delegreturn? That too can be called from nfs4_evict_inode...

--
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com

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