Re: [PATCH] SUNRPC: Fix locking around callback channel reply receive

[Jeff Layton <jeff.layton@primarydata.com>]

On Wed, 12 Nov 2014 18:04:04 -0500
Trond Myklebust <trond.myklebust@primarydata.com> wrote:

> Both xprt_lookup_rqst() and xprt_complete_rqst() require that you
> take the transport lock in order to avoid races with xprt_transmit().
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
> Cc: Bruce Fields <bfields@fieldses.org>
> ---
>  net/sunrpc/svcsock.c | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 3f959c681885..f9c052d508f0 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -1019,17 +1019,12 @@ static int receive_cb_reply(struct svc_sock *svsk, struct svc_rqst *rqstp)
>  	xid = *p++;
>  	calldir = *p;
>  
> -	if (bc_xprt)
> -		req = xprt_lookup_rqst(bc_xprt, xid);
> -
> -	if (!req) {
> -		printk(KERN_NOTICE
> -			"%s: Got unrecognized reply: "
> -			"calldir 0x%x xpt_bc_xprt %p xid %08x\n",
> -			__func__, ntohl(calldir),
> -			bc_xprt, ntohl(xid));
> +	if (!bc_xprt)
>  		return -EAGAIN;
> -	}
> +	spin_lock_bh(&bc_xprt->transport_lock);
> +	req = xprt_lookup_rqst(bc_xprt, xid);
> +	if (!req)
> +		goto unlock_notfound;
>  
>  	memcpy(&req->rq_private_buf, &req->rq_rcv_buf, sizeof(struct xdr_buf));
>  	/*
> @@ -1040,11 +1035,21 @@ static int receive_cb_reply(struct svc_sock *svsk, struct svc_rqst *rqstp)
>  	dst = &req->rq_private_buf.head[0];
>  	src = &rqstp->rq_arg.head[0];
>  	if (dst->iov_len < src->iov_len)
> -		return -EAGAIN; /* whatever; just giving up. */
> +		goto unlock_eagain; /* whatever; just giving up. */
>  	memcpy(dst->iov_base, src->iov_base, src->iov_len);
>  	xprt_complete_rqst(req->rq_task, rqstp->rq_arg.len);
>  	rqstp->rq_arg.len = 0;
> +	spin_unlock_bh(&bc_xprt->transport_lock);
>  	return 0;
> +unlock_notfound:
> +	printk(KERN_NOTICE
> +		"%s: Got unrecognized reply: "
> +		"calldir 0x%x xpt_bc_xprt %p xid %08x\n",
> +		__func__, ntohl(calldir),
> +		bc_xprt, ntohl(xid));
> +unlock_eagain:
> +	spin_unlock_bh(&bc_xprt->transport_lock);
> +	return -EAGAIN;
>  }
>  
>  static int copy_pages_to_kvecs(struct kvec *vec, struct page **pages, int len)

Nice catch. It would also be good to pair this with a
lockdep_assert_held() call in xprt_lookup_rqst, but that could be added
in a separate patch.

Reviewed-by: Jeff Layton <jlayton@primarydata.com>