linux-kernel - Re: [PATCH 2/3] SUNRPC: check rpcbind clients usage counter before decrement

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Date:	Mon, 30 Apr 2012 17:45:04 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH 2/3] SUNRPC: check rpcbind clients usage counter before
 decrement

On Fri, Apr 27, 2012 at 06:08:13PM +0400, Stanislav Kinsbursky wrote:
> On 27.04.2012 17:55, J. Bruce Fields wrote:
> >On Wed, Apr 25, 2012 at 05:37:49PM +0400, Stanislav Kinsbursky wrote:
> >>Registering service with svc_bind() can fail. In this case service will be
> >>destroyed and during destruction it will try to unregister itself from rpcbind.
> >>In this case unregister have to be skipped.
> >
> >Isn't this a preexisting bug, in which case perhaps Trond should at it
> >to his list of bugs to submit now?
> >
> 
> Not it's not.
> 
> Previously, in case of bind operations failure, rpcb_put_local()
> wasn't called, but service data was destroyed instead:
> 
> -	if (svc_uses_rpcbind(serv)) {
> -		if (svc_rpcb_setup(serv, current->nsproxy->net_ns) < 0) {
> -			kfree(serv->sv_pools);
> -			kfree(serv);
> -			return NULL;
> -		}
> -		if (!serv->sv_shutdown)
> -			serv->sv_shutdown = svc_rpcb_cleanup;
> -	}
> 
> Now (with svc_bind() introduction) service can be created, but
> svc_bind() could fail. And thus svc_destroy() have to be called.
> Which will call rpcb_put_local().
> 
> And the problem here that svc_bind() can fail before incrementing of
> rpcb usage counter.

OK, but then you're fixing a bug that you just introduced with the
previous patch.

So this should be combined with the previous patch.

--b.

> 
> >--b.
> >
> >>
> >>Signed-off-by: Stanislav Kinsbursky<skinsbursky@...allels.com>
> >>
> >>---
> >>  net/sunrpc/rpcb_clnt.c |   12 +++++++-----
> >>  1 files changed, 7 insertions(+), 5 deletions(-)
> >>
> >>diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
> >>index 78ac39f..4c38b33 100644
> >>--- a/net/sunrpc/rpcb_clnt.c
> >>+++ b/net/sunrpc/rpcb_clnt.c
> >>@@ -180,14 +180,16 @@ void rpcb_put_local(struct net *net)
> >>  	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
> >>  	struct rpc_clnt *clnt = sn->rpcb_local_clnt;
> >>  	struct rpc_clnt *clnt4 = sn->rpcb_local_clnt4;
> >>-	int shutdown;
> >>+	int shutdown = 0;
> >>
> >>  	spin_lock(&sn->rpcb_clnt_lock);
> >>-	if (--sn->rpcb_users == 0) {
> >>-		sn->rpcb_local_clnt = NULL;
> >>-		sn->rpcb_local_clnt4 = NULL;
> >>+	if (sn->rpcb_users) {
> >>+		if (--sn->rpcb_users == 0) {
> >>+			sn->rpcb_local_clnt = NULL;
> >>+			sn->rpcb_local_clnt4 = NULL;
> >>+		}
> >>+		shutdown = !sn->rpcb_users;
> >>  	}
> >>-	shutdown = !sn->rpcb_users;
> >>  	spin_unlock(&sn->rpcb_clnt_lock);
> >>
> >>  	if (shutdown) {
> >>
> 
> 
> -- 
> Best regards,
> Stanislav Kinsbursky
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