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From:   Wenbin Zeng <wenbin.zeng@gmail.com>
To:     viro@zeniv.linux.org.uk, davem@davemloft.net, bfields@fieldses.org,
        jlayton@kernel.org, trond.myklebust@hammerspace.com,
        anna.schumaker@netapp.com, wenbinzeng@tencent.com,
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        tyhicks@canonical.com, chuck.lever@oracle.com, neilb@suse.com
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-nfs@vger.kernel.org
Subject: [PATCH 3/3] auth_gss: fix deadlock that blocks rpcsec_gss_exit_net when use-gss-proxy==1
Date:   Wed,  1 May 2019 14:42:25 +0800
Message-Id: <1556692945-3996-4-git-send-email-wenbinzeng@tencent.com>
In-Reply-To: <1556692945-3996-1-git-send-email-wenbinzeng@tencent.com>
References: <1556692945-3996-1-git-send-email-wenbinzeng@tencent.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

When use-gss-proxy is set to 1, write_gssp() creates a rpc client in
gssp_rpc_create(), this increases netns refcount by 2, these refcounts are
supposed to be released in rpcsec_gss_exit_net(), but it will never happen
because rpcsec_gss_exit_net() is triggered only when netns refcount gets
to 0, specifically:
    refcount=0 -> cleanup_net() -> ops_exit_list -> rpcsec_gss_exit_net
It is a deadlock situation here, refcount will never get to 0 unless
rpcsec_gss_exit_net() is called.

This fix introduced a new callback i.e. evict in struct proc_ns_operations,
which is called in nsfs_evict. Moving rpcsec_gss_exit_net to evict path
gives it a chance to get called and avoids the above deadlock situation.

Signed-off-by: Wenbin Zeng <wenbinzeng@tencent.com>
---
 net/sunrpc/auth_gss/auth_gss.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 3fd56c0..3e6bd59 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -2136,14 +2136,17 @@ static __net_init int rpcsec_gss_init_net(struct net *net)
 	return gss_svc_init_net(net);
 }
 
-static __net_exit void rpcsec_gss_exit_net(struct net *net)
+static void rpcsec_gss_evict_net(struct net *net)
 {
-	gss_svc_shutdown_net(net);
+	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+	if (sn->gssp_clnt)
+		gss_svc_shutdown_net(net);
 }
 
 static struct pernet_operations rpcsec_gss_net_ops = {
 	.init = rpcsec_gss_init_net,
-	.exit = rpcsec_gss_exit_net,
+	.evict = rpcsec_gss_evict_net,
 };
 
 /*
-- 
1.8.3.1