linux-kernel - Re: [NFS] 2.6.17.8 - do_vfs_lock: VFS is out of sync with lock manager!

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Date:	Mon, 21 Aug 2006 15:54:58 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Neil Brown <neilb@...e.de>
Cc:	Jesper Juhl <jesper.juhl@...il.com>, nfs@...ts.sourceforge.net,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [NFS] 2.6.17.8 - do_vfs_lock: VFS is out of sync with lock
	manager!

On Mon, 2006-08-21 at 13:34 +1000, Neil Brown wrote:
> Looking in fs/nfs/file.c (at 2.6.18-rc4-mm1 if it matters, but 2.6.17
> is much the same)
> 
>  - do_vfs_lock is only called when the filesystem was mounted with
>     -o nolock  EXCEPT
>  - If a lock request to the server in interrupted (when mounted with
>      -o intr) then do_vfs_lock is called to try to get the lock
>     locally.  Normally equivalent code will be called inside
>     fs/lockd/clntproc.c when the server replies that the lock has been
>     gained.  In the case of an interrupt though this doesn't happen
>     but the lock may still have happened on the server.  So we record
>     locally that the lock was gained, to ensure that it gets unlocked
>     when the process exits.
> 
> As you don't have '-o nolocks' you must be hitting the second case.
> The lock call to the server returns -EINTR or -ERESTARTSYS and
> do_vfs_lock is called just-in-case.  
> As this is a just-in-case call, it is quite possible that the lock is
> held by some other process, so getting an error is entirely possible.
> So printing the message in this case seems wrong.
> 
> On the other hand, printing the message in any other case seems wrong
> too, as server locking is not being used, so there is nothing to get
> out of sync with.
> 
> As a further complication, I don't think that in the just-in-case
> situation that it should risk waiting for the lock.
> Now maybe we can be sure there is a pending signal which will break
> out of any wait (though I'm worried about -ERESTARTSYS - that doesn't
> imply a signal does it?), but I would feel more comfortable if
> FL_SLEEP were turned off in that path.
> 
> So: Trond:  Any obvious errors in the above?
> Is the following patch ok?

Could we instead replace it with a dprintk() that returns the value of
"res"? That will keep it useful for debugging purposes.

Cheers,
  Trond

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