Messages in this thread | | | Subject | Re: [PATCH] SUNRPC: Allow one callback request to be received from two sk_buff | From | Trond Myklebust <> | Date | Tue, 21 Jan 2014 08:35:36 -0700 |
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On Jan 21, 2014, at 3:08, shaobingqing <shaobingqing@bwstor.com.cn> wrote:
> 2014/1/21 Trond Myklebust <trond.myklebust@primarydata.com>: >> 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. > > 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.
> 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
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