linux-kernel - Re: [PATCH] SUNRPC: Allow one callback request to be received from two sk

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Date:	Mon, 20 Jan 2014 16:17:23 -0700
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	shaobingqing <shaobingqing@...tor.com.cn>
Cc:	bfields@...hat.com, davem@...emloft.net, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] SUNRPC: Allow one callback request to be received from
 two sk_buff

On Mon, 2014-01-20 at 14:59 +0800, shaobingqing wrote:
> In current code, there only one struct rpc_rqst is prealloced. If one 
> callback request is received from two sk_buff, the xprt_alloc_bc_request
> would be execute two times with the same transport->xid. The first time
> xprt_alloc_bc_request will alloc one struct rpc_rqst and the TCP_RCV_COPY_DATA
> bit of transport->tcp_flags will not be cleared. The second time 
> xprt_alloc_bc_request could not alloc struct rpc_rqst any more and NULL
> pointer will be returned, then xprt_force_disconnect occur. I think one 
> callback request can be allowed to be received from two sk_buff.
> 
> Signed-off-by: shaobingqing <shaobingqing@...tor.com.cn>
> ---
>  net/sunrpc/xprtsock.c |   11 +++++++++--
>  1 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index ee03d35..606950d 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -1271,8 +1271,13 @@ static inline int xs_tcp_read_callback(struct rpc_xprt *xprt,
>  	struct sock_xprt *transport =
>  				container_of(xprt, struct sock_xprt, xprt);
>  	struct rpc_rqst *req;
> +	static struct rpc_rqst *req_partial;
> +
> +	if (req_partial == NULL)
> +		req = xprt_alloc_bc_request(xprt);
> +	else if (req_partial->rq_xid == transport->tcp_xid)
> +		req = req_partial;

What happens here if req_partial->rq_xid != transport->tcp_xid? AFAICS,
req will be undefined. Either way, you cannot use a static variable for
storage here: that isn't re-entrant.

> -	req = xprt_alloc_bc_request(xprt);
>  	if (req == NULL) {
>  		printk(KERN_WARNING "Callback slot table overflowed\n");
>  		xprt_force_disconnect(xprt);
> @@ -1285,6 +1290,7 @@ static inline int xs_tcp_read_callback(struct rpc_xprt *xprt,
>  
>  	if (!(transport->tcp_flags & TCP_RCV_COPY_DATA)) {
>  		struct svc_serv *bc_serv = xprt->bc_serv;
> +		req_partial = NULL;
>  
>  		/*
>  		 * Add callback request to callback list.  The callback
> @@ -1297,7 +1303,8 @@ static inline int xs_tcp_read_callback(struct rpc_xprt *xprt,
>  		list_add(&req->rq_bc_list, &bc_serv->sv_cb_list);
>  		spin_unlock(&bc_serv->sv_cb_lock);
>  		wake_up(&bc_serv->sv_cb_waitq);
> -	}
> +	} else
> +		req_partial = req;
>  
>  	req->rq_private_buf.len = transport->tcp_copied;
>  


-- 
Trond Myklebust
Linux NFS client maintainer

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