> -----Original Message----- > From: Jeff Layton [mailto:jlayton@xxxxxxxxxx] > Sent: Tuesday, September 20, 2011 10:25 AM > To: Stanislav Kinsbursky > Cc: Myklebust, Trond; linux-nfs@xxxxxxxxxxxxxxx; Pavel Emelianov; > neilb@xxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > bfields@xxxxxxxxxxxx; davem@xxxxxxxxxxxxx > Subject: Re: [PATCH v5 1/8] SUNRPC: introduce helpers for reference > counted rpcbind clients > > On Tue, 20 Sep 2011 17:49:27 +0400 > Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx> wrote: > > > v5: fixed races with rpcb_users in rpcb_get_local() > > > > This helpers will be used for dynamical creation and destruction of > > rpcbind clients. > > Variable rpcb_users is actually a counter of lauched RPC services. If > > rpcbind clients has been created already, then we just increase rpcb_users. > > > > Signed-off-by: Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx> > > > > --- > > net/sunrpc/rpcb_clnt.c | 53 > ++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 files changed, 53 insertions(+), 0 deletions(-) > > > > diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c index > > e45d2fb..5f4a406 100644 > > --- a/net/sunrpc/rpcb_clnt.c > > +++ b/net/sunrpc/rpcb_clnt.c > > @@ -114,6 +114,9 @@ static struct rpc_program rpcb_program; > > static struct rpc_clnt * rpcb_local_clnt; > > static struct rpc_clnt * rpcb_local_clnt4; > > +DEFINE_SPINLOCK(rpcb_clnt_lock); > > +unsigned int rpcb_users; > > + > > struct rpcbind_args { > > struct rpc_xprt * r_xprt; > > @@ -161,6 +164,56 @@ static void rpcb_map_release(void *data) > > kfree(map); > > } > > +static int rpcb_get_local(void) > > +{ > > + int cnt; > > + > > + spin_lock(&rpcb_clnt_lock); > > + if (rpcb_users) > > + rpcb_users++; > > + cnt = rpcb_users; > > + spin_unlock(&rpcb_clnt_lock); > > + > > + return cnt; > > +} > > + > > +void rpcb_put_local(void) > > +{ > > + struct rpc_clnt *clnt = rpcb_local_clnt; > > + struct rpc_clnt *clnt4 = rpcb_local_clnt4; > > + int shutdown; > > + > > + spin_lock(&rpcb_clnt_lock); > > + if (--rpcb_users == 0) { > > + rpcb_local_clnt = NULL; > > + rpcb_local_clnt4 = NULL; > > + } > > In the function below, you mention that the above pointers are protected by > rpcb_create_local_mutex, but it looks like they get reset here without that > being held? > > Might it be simpler to just protect rpcb_users with the > rpcb_create_local_mutex and ensure that it's held whenever you call one of > these routines? None of these are codepaths are particularly hot. Alternatively, if you do if (rpcb_users == 1) { rpcb_local_clnt = NULL; rpcb_local_clnt4 = NULL; smp_wmb(); rpcb_users = 0; } else rpcb_users--; then the spinlock protection in rpbc_get_local() is still good enough to guarantee correctness. -- 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
