2019-04-07 11:40:59

by 易林

Subject: should the svc_xprt_get called after th e object assigned to a global variable？

Hi, all:
when analyzing the v5.1 source code, I notice that in function nfsd4_process_cb_update,
the object c->cn_xprt assigned to a local variable conn.cb_xprt with a refcount increased:
if (c) {
svc_xprt_get(c->cn_xprt);
conn.cb_xprt = c->cn_xprt;
ses = c->cn_session;
}

and the variable conn.cb_xprt will be assigned to a global object clp->cl_cb_conn.cb_xprt
in callee setup_callback_client with a condition that clp->cl_minorversion != 0:

if (clp->cl_minorversion == 0) {
if (!clp->cl_cred.cr_principal &&
(clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
return -EINVAL;
args.client_name = clp->cl_cred.cr_principal;
args.prognumber = conn->cb_prog;
args.protocol = XPRT_TRANSPORT_TCP;
args.authflavor = clp->cl_cred.cr_flavor;
clp->cl_cb_ident = conn->cb_ident;
} else {
if (!conn->cb_xprt)
return -EINVAL;
clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
clp->cl_cb_session = ses;
args.bc_xprt = conn->cb_xprt;
args.prognumber = clp->cl_cb_session->se_cb_prog;
args.protocol = conn->cb_xprt->xpt_class->xcl_ident |
XPRT_TRANSPORT_BC;
args.authflavor = ses->se_cb_sec.flavor;
}

what if the cl_minorversion equals 0 ? the c->cn_xprt's refcount will increased without a assignment.
Can it be ensured that the cl_minorversion won't be zero with the refcount increment?

Best Regards

Lin Yi

2019-04-08 16:27:19

by J. Bruce Fields

Subject: Re: should the svc_xprt_get call ed after the object assigned to a global variable？

On Sun, Apr 07, 2019 at 07:40:43PM +0800, 易林 wrote:
> Hi, all:
> when analyzing the v5.1 source code, I notice that in function nfsd4_process_cb_update,
> the object c->cn_xprt assigned to a local variable conn.cb_xprt with a refcount increased:
> if (c) {
> svc_xprt_get(c->cn_xprt);
> conn.cb_xprt = c->cn_xprt;
> ses = c->cn_session;
> }
>
> and the variable conn.cb_xprt will be assigned to a global object clp->cl_cb_conn.cb_xprt
> in callee setup_callback_client with a condition that clp->cl_minorversion != 0:
>
> if (clp->cl_minorversion == 0) {
> if (!clp->cl_cred.cr_principal &&
> (clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
> return -EINVAL;
> args.client_name = clp->cl_cred.cr_principal;
> args.prognumber = conn->cb_prog;
> args.protocol = XPRT_TRANSPORT_TCP;
> args.authflavor = clp->cl_cred.cr_flavor;
> clp->cl_cb_ident = conn->cb_ident;
> } else {
> if (!conn->cb_xprt)
> return -EINVAL;
> clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
> clp->cl_cb_session = ses;
> args.bc_xprt = conn->cb_xprt;
> args.prognumber = clp->cl_cb_session->se_cb_prog;
> args.protocol = conn->cb_xprt->xpt_class->xcl_ident |
> XPRT_TRANSPORT_BC;
> args.authflavor = ses->se_cb_sec.flavor;
> }
>
> what if the cl_minorversion equals 0 ? the c->cn_xprt's refcount will increased without a assignment.
> Can it be ensured that the cl_minorversion won't be zero with the refcount increment?

Sessions were introduced with NFSv4.1, __nfsd4_find_backchannel should
always find clp->cl_sessions empty in the 4.0 case.

So I think it's OK. Not the clearest code ever, though. I wonder if it
would make sense to separate the 4.0 and 4.1 codepaths earlier on, given
how little code they share.

--b.