2014/1/23 J. Bruce Fields <bfields@xxxxxxxxxxxx>: > On Tue, Jan 21, 2014 at 08:35:36AM -0700, Trond Myklebust wrote: >> >> On Jan 21, 2014, at 3:08, shaobingqing <shaobingqing@xxxxxxxxxxxxx> wrote: >> >> > 2014/1/21 Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>: >> >> 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@xxxxxxxxxxxxx> >> >>> --- >> >>> 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. >> > >> > Because metadata sever only have one slot for backchannel request, >> > req_partial->rq_xid == transport->tcp_xid always happens, if the callback >> > request just being splited in two sk_buffs. But req_partial->rq_xid != >> > transport->tcp_xid may also happens in some special cases, such as >> > retransmission occurs? >> >> If the server retransmits, then it is broken. The NFSv4.1 protocol does not allow it to retransmit unless the connection breaks. > > shaobingqing, are you actually seeing retransmission? (If so, are we > setting up the callback client wrong?) No, not actually. Here I just see that one client can receive two callback requests with the same xid. > > --b. > >> >> > If one callback request is splited in two sk_buffs, xs_tcp_read_callback >> > will be execute two times. The req_partial should be a static variable, >> > because the second execution of xs_tcp_read_callback should use >> > the rpc_rqst allocated for the first execution, which saves information >> > copies from the first sk_buff. >> >> No! This is a multi-threaded/process environment which can support multiple connection. It is a bug to use a static variable. >> >> -- >> Trond Myklebust >> Linux NFS client maintainer >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
