netdev - Re: [PATCH net] net_sched: gen_estimator: fix lockdep splat

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Date:   Mon, 29 Jan 2018 14:31:08 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us
Subject: Re: [PATCH net] net_sched: gen_estimator: fix lockdep splat

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 27 Jan 2018 10:58:43 -0800

> From: Eric Dumazet <edumazet@...gle.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@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied, thanks.