Date: Tue, 22 Jul 2014 13:45:52 -0400
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Jeff Layton <jlayton@primarydata.com>
Cc: linux-nfs@vger.kernel.org
Subject: Re: [PATCH] nfsd: bump dp->dl_time when unhashing delegation
Message-ID: <20140722174552.GA27277@fieldses.org>
References: <1406047291-1279-1-git-send-email-jlayton@primarydata.com>
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On Tue, Jul 22, 2014 at 12:41:31PM -0400, Jeff Layton wrote:
> There's a potential race between a lease break and DELEGRETURN call.
> 
> Suppose a lease break comes in and queues the workqueue job for a
> delegation, but it doesn't run just yet. Then, a DELEGRETURN comes in
> finds the delegation and calls destroy_delegation on it to unhash it and
> put its primary reference.
> 
> Next, the workqueue job runs and queues the delegation back onto the
> del_recall_lru list, issues the CB_RECALL and puts the final reference.
> With that, the final reference to the delegation is put, but it's still
> on the LRU list.
> 
> When we go to unhash a delegation, it's because we intend to get rid of
> it soon afterward, so we don't want lease breaks to mess with it once
> that occurs. Fix this by bumping the dl_time whenever we unhash a
> delegation, to ensure that lease breaks don't monkey with it.

Makes sense, thanks.  Repeating from IRC: this fixes a regression from
02e1215f9f7 "nfsd: Avoid taking state_lock while holding inode lock in
nfsd_break_one_deleg".  (In my tree only.)

--b.

> 
> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
> ---
>  fs/nfsd/nfs4state.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 72da0d44e66b..a3a828d17563 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -660,6 +660,8 @@ unhash_delegation(struct nfs4_delegation *dp)
>  
>  	spin_lock(&state_lock);
>  	dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
> +	/* Ensure that deleg break won't try to requeue it */
> +	++dp->dl_time;
>  	spin_lock(&fp->fi_lock);
>  	list_del_init(&dp->dl_perclnt);
>  	list_del_init(&dp->dl_recall_lru);
> -- 
> 1.9.3
>