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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     WANG Cong <xiyou.wangcong@gmail.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 073/293] net_sched: move tcf_lock down after
 gen_replace_estimator()
Thread-Topic: [PATCH AUTOSEL for 4.9 073/293] net_sched: move tcf_lock down
 after gen_replace_estimator()
Thread-Index: AQHTz5kI5bHtrvQjqUOFH/ek0xZDHw==
Date:   Mon, 9 Apr 2018 00:23:51 +0000
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From: WANG Cong <xiyou.wangcong@gmail.com>

[ Upstream commit 74030603dfd9f76c0f279f19f1dd1ee3028fee7a ]

Laura reported a sleep-in-atomic kernel warning inside
tcf_act_police_init() which calls gen_replace_estimator() with
spinlock protection.

It is not necessary in this case, we already have RTNL lock here
so it is enough to protect concurrent writers. For the reader,
i.e. tcf_act_police(), it needs to make decision based on this
rate estimator, in the worst case we drop more/less packets than
necessary while changing the rate in parallel, it is still acceptable.

Reported-by: Laura Abbott <labbott@redhat.com>
Reported-by: Nick Huber <nicholashuber@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 net/sched/act_police.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/sched/act_police.c b/net/sched/act_police.c
index d1bd248fe146..ca30796290aa 100644
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -132,22 +132,22 @@ static int tcf_act_police_init(struct net *net, struc=
t nlattr *nla,
 		}
 	}
=20
-	spin_lock_bh(&police->tcf_lock);
 	if (est) {
 		err =3D gen_replace_estimator(&police->tcf_bstats, NULL,
 					    &police->tcf_rate_est,
 					    &police->tcf_lock,
 					    NULL, est);
 		if (err)
-			goto failure_unlock;
+			goto failure;
 	} else if (tb[TCA_POLICE_AVRATE] &&
 		   (ret =3D=3D ACT_P_CREATED ||
 		    !gen_estimator_active(&police->tcf_bstats,
 					  &police->tcf_rate_est))) {
 		err =3D -EINVAL;
-		goto failure_unlock;
+		goto failure;
 	}
=20
+	spin_lock_bh(&police->tcf_lock);
 	/* No failure allowed after this point */
 	police->tcfp_mtu =3D parm->mtu;
 	if (police->tcfp_mtu =3D=3D 0) {
@@ -193,8 +193,6 @@ static int tcf_act_police_init(struct net *net, struct =
nlattr *nla,
=20
 	return ret;
=20
-failure_unlock:
-	spin_unlock_bh(&police->tcf_lock);
 failure:
 	qdisc_put_rtab(P_tab);
 	qdisc_put_rtab(R_tab);
--=20
2.15.1