[Devel] [PATCH RH7] ms/net_sched: gen_estimator: fix lockdep splat

[Vasily Averin]

From: Eric Dumazet <edumazet at google.com>

syzbot reported a lockdep splat in gen_new_estimator() /
est_fetch_counters() when attempting to lock est->stats_lock.

Since est_fetch_counters() is called from BH context from timer
interrupt, we need to block BH as well when calling it from process
context.

Most qdiscs use per cpu counters and are immune to the problem,
but net/sched/act_api.c and net/netfilter/xt_RATEEST.c are using
a spinlock to protect their data. They both call gen_new_estimator()
while object is created and not yet alive, so this bug could
not trigger a deadlock, only a lockdep splat.

Fixes: 1c0d32fde5bd ("net_sched: gen_estimator: complete rewrite of rate estimators")
Signed-off-by: Eric Dumazet <edumazet at google.com>
Reported-by: syzbot <syzkaller at googlegroups.com>
Acked-by: Cong Wang <xiyou.wangcong at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>

(cherry-picked from commit 40ca54e3a686f13117f3de0c443f8026dadf7c44)
https://jira.sw.ru/browse/PSBM-123087
Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 net/core/gen_estimator.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
index bca1d06..0e3024c 100644
--- a/net/core/gen_estimator.c
+++ b/net/core/gen_estimator.c
@@ -159,7 +159,11 @@ int gen_new_estimator(struct gnet_stats_basic_packed *bstats,
 	est->intvl_log = intvl_log;
 	est->cpu_bstats = cpu_bstats;
 
+	if (stats_lock)
+		local_bh_disable();
 	est_fetch_counters(est, &b);
+	if (stats_lock)
+		local_bh_enable();
 	est->last_bytes = b.bytes;
 	est->last_packets = b.packets;
 	old = rcu_dereference_protected(*rate_est, 1);
-- 
1.8.3.1