From: Frank Filz <ffilzlnx@us.ibm.com>
Subject: Re: [PATCH] Make sure unlock is really an
	unlock	when	cancelling a lock
Date: Wed, 13 Jun 2007 13:17:37 -0700
Message-ID: <1181765857.16851.16.camel@dyn9047022153>
References: <1181581269.8988.42.camel@dyn9047022153>
	<1181752511.6151.5.camel@heimdal.trondhjem.org>
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Cc: NFS List <nfs@lists.sourceforge.net>
To: Trond Myklebust <trond.myklebust@fys.uio.no>
In-Reply-To: <1181752511.6151.5.camel@heimdal.trondhjem.org>
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On Wed, 2007-06-13 at 12:35 -0400, Trond Myklebust wrote:
> On Mon, 2007-06-11 at 10:01 -0700, Frank Filz wrote:
> > I ran into a curious issue when a lock is being canceled. The
> > cancellation results in a lock request to the vfs layer instead of an
> > unlock request. This is particularly insidious when the process that
> 
> Any idea why the cancellation turns into a lock request? I really don't
> want to apply a patch that just appears to paper over the problem.

Ok, the path is as follows:

first _nfs4_do_setlk():

static int _nfs4_do_setlk(struct nfs4_state *state, int cmd, struct file_lock *fl, int reclaim)
...
	ret = nfs4_wait_for_completion_rpc_task(task);
	if (ret == 0) {
...
	} else
		data->cancelled = 1;

then nfs4_lock_release():

static void nfs4_lock_release(void *calldata)
...
	if (data->cancelled != 0) {
		struct rpc_task *task;
		task = nfs4_do_unlck(&data->fl, data->ctx, data->lsp,
				data->arg.lock_seqid);

The problem is the same file_lock that was passed in to _nfs4_do_setlk()
gets passed to nfs4_do_unlck() from nfs4_lock_release(). So the type is
still F_RDLCK or FWRLCK, not F_UNLCK. At some point, when cancelling the
lock, the type needs to be changed to F_UNLCK. It seemed easiest to do
that in nfs4_do_unlck(), but it could be done in nfs4_lock_release().
The concern I had with doing it there was if something still needed the
original file_lock, though it turns out the original file_lock still
needs to be modified by nfs4_do_unlck() because nfs4_do_unlck() uses the
original file_lock to pass to the vfs layer, and a copy of the original
file_lock for the RPC request.

Frank


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