Re: [PATCH] SUNRPC: Allow one callback request to be received from two sk_buff

Trond Myklebust
2014-01-20T23:17:28Z

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@bwstor.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