[PATCH AUTOSEL for 3.18 030/101] net_sched: move tcf_lock down after gen_replace_estimator()

[Sasha Levin]

From: WANG Cong <xiyou.wangc...@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 <labb...@redhat.com>
Reported-by: Nick Huber <nicholashu...@gmail.com>
Cc: Jamal Hadi Salim <j...@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
Acked-by: Jamal Hadi Salim <j...@mojatatu.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Sasha Levin <alexander.le...@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 69791ca77a05..1a25d25b9a56 100644
--- a/net/sched/act_police.c
+++ b/net/sched/act_police.c
@@ -176,21 +176,21 @@ override:
                }
        }
 
-       spin_lock_bh(&police->tcf_lock);
        if (est) {
                err = gen_replace_estimator(&police->tcf_bstats, NULL,
                                            &police->tcf_rate_est,
                                            &police->tcf_lock, est);
                if (err)
-                       goto failure_unlock;
+                       goto failure;
        } else if (tb[TCA_POLICE_AVRATE] &&
                   (ret == ACT_P_CREATED ||
                    !gen_estimator_active(&police->tcf_bstats,
                                          &police->tcf_rate_est))) {
                err = -EINVAL;
-               goto failure_unlock;
+               goto failure;
        }
 
+       spin_lock_bh(&police->tcf_lock);
        /* No failure allowed after this point */
        police->tcfp_mtu = parm->mtu;
        if (police->tcfp_mtu == 0) {
@@ -242,8 +242,6 @@ override:
        a->priv = police;
        return ret;
 
-failure_unlock:
-       spin_unlock_bh(&police->tcf_lock);
 failure:
        qdisc_put_rtab(P_tab);
        qdisc_put_rtab(R_tab);
-- 
2.15.1