Date:   Mon, 22 Apr 2019 15:46:08 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Jeff Layton <jlayton@kernel.org>
Cc:     slawek1211@gmail.com, neilb@suse.com, linux-nfs@vger.kernel.org
Subject: Re: [PATCH v2 2/2] nfsd: wake blocked file lock waiters before
 sending callback
Message-ID: <20190422194608.GB25280@fieldses.org>
References: <20190422163424.19402-1-jlayton@kernel.org>
 <20190422163424.19402-3-jlayton@kernel.org>
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On Mon, Apr 22, 2019 at 12:34:24PM -0400, Jeff Layton wrote:
> When a blocked NFS lock is "awoken" we send a callback to the server and
> then wake any hosts waiting on it. If a client attempts to get a lock
> and then drops off the net, we could end up waiting for a long time
> until we end up waking locks blocked on that request.
> 
> Add a new "prepare" phase for CB_NOTIFY_LOCK callbacks, and have it
> call locks_delete_block to wake any lock requests waiting on the
> one for which we're sending the callback before it is sent.

How about this for the wording of that last sentence:

	So, wake any other waiting lock requests before sending the
	callback.  Do this by calling locks_delete_block in a new
	"prepare" phase for CB_NOTIFY_LOCK callbacks.

Come to think of that, the second sentence is redundant with the code; I
think I'll just go with the first.

Committing with that.

Thanks for working this out, and thanks to Slawomir Pryczek for the
reproducer.

--b.

> 
> URL: https://bugzilla.kernel.org/show_bug.cgi?id=203363
> Fixes: 16306a61d3b7 ("fs/locks: always delete_block after waiting.")
> Reported-by: Slawomir Pryczek <slawek1211@gmail.com>
> Cc: Neil Brown <neilb@suse.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/nfsd/nfs4state.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index e87e15df2044..f056b1d3fecd 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -298,6 +298,14 @@ remove_blocked_locks(struct nfs4_lockowner *lo)
>  	}
>  }
>  
> +static void
> +nfsd4_cb_notify_lock_prepare(struct nfsd4_callback *cb)
> +{
> +	struct nfsd4_blocked_lock	*nbl = container_of(cb,
> +						struct nfsd4_blocked_lock, nbl_cb);
> +	locks_delete_block(&nbl->nbl_lock);
> +}
> +
>  static int
>  nfsd4_cb_notify_lock_done(struct nfsd4_callback *cb, struct rpc_task *task)
>  {
> @@ -325,6 +333,7 @@ nfsd4_cb_notify_lock_release(struct nfsd4_callback *cb)
>  }
>  
>  static const struct nfsd4_callback_ops nfsd4_cb_notify_lock_ops = {
> +	.prepare	= nfsd4_cb_notify_lock_prepare,
>  	.done		= nfsd4_cb_notify_lock_done,
>  	.release	= nfsd4_cb_notify_lock_release,
>  };
> -- 
> 2.20.1