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net_sched: gen_estimator: fix lockdep splat

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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@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2018-01-27 10:58:43 -08:00 committed by David S. Miller
parent 032dc41ba6
commit 40ca54e3a6
1 changed files with 4 additions and 0 deletions
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4
net/core/gen_estimator.c
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@ -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);