netdev - Re: [PATCH] net: sched: suspicious RCU usage in qdisc

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Date:	Fri, 3 Oct 2014 15:22:39 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	John Fastabend <john.fastabend@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sched: suspicious RCU usage in qdisc_watchdog

On Thu, Oct 2, 2014 at 10:43 PM, John Fastabend
<john.fastabend@...il.com> wrote:
> Suspicious RCU usage in qdisc_watchdog call needs to be done inside
> rcu_read_lock/rcu_read_unlock. And then Qdisc destroy operations
> need to ensure timer is cancelled before removing qdisc structure.

More precisely, qdisc_root().

>
> [ 3992.191339] ===============================
> [ 3992.191340] [ INFO: suspicious RCU usage. ]
> [ 3992.191343] 3.17.0-rc6net-next+ #72 Not tainted
> [ 3992.191345] -------------------------------
> [ 3992.191347] include/net/sch_generic.h:272 suspicious rcu_dereference_check() usage!
> [ 3992.191348]
> [ 3992.191348] other info that might help us debug this:
> [ 3992.191348]
> [ 3992.191351]
> [ 3992.191351] rcu_scheduler_active = 1, debug_locks = 1
> [ 3992.191353] no locks held by swapper/1/0.
> [ 3992.191355]
> [ 3992.191355] stack backtrace:
> [ 3992.191358] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.17.0-rc6net-next+ #72
> [ 3992.191360] Hardware name:                  /DZ77RE-75K, BIOS GAZ7711H.86A.0060.2012.1115.1750 11/15/2012
> [ 3992.191362]  0000000000000001 ffff880235803e48 ffffffff8178f92c 0000000000000000
> [ 3992.191366]  ffff8802322224a0 ffff880235803e78 ffffffff810c9966 ffff8800a5fe3000
> [ 3992.191370]  ffff880235803f30 ffff8802359cd768 ffff8802359cd6e0 ffff880235803e98
> [ 3992.191374] Call Trace:
> [ 3992.191376]  <IRQ>  [<ffffffff8178f92c>] dump_stack+0x4e/0x68
> [ 3992.191387]  [<ffffffff810c9966>] lockdep_rcu_suspicious+0xe6/0x130
> [ 3992.191392]  [<ffffffff8167213a>] qdisc_watchdog+0x8a/0xb0
> [ 3992.191396]  [<ffffffff810f93f2>] __run_hrtimer+0x72/0x420
> [ 3992.191399]  [<ffffffff810f9bcd>] ? hrtimer_interrupt+0x7d/0x240
> [ 3992.191403]  [<ffffffff816720b0>] ? tc_classify+0xc0/0xc0
> [ 3992.191406]  [<ffffffff810f9c4f>] hrtimer_interrupt+0xff/0x240
> [ 3992.191410]  [<ffffffff8109e4a5>] ? __atomic_notifier_call_chain+0x5/0x140
> [ 3992.191415]  [<ffffffff8103577b>] local_apic_timer_interrupt+0x3b/0x60
> [ 3992.191419]  [<ffffffff8179c2b5>] smp_apic_timer_interrupt+0x45/0x60
> [ 3992.191422]  [<ffffffff8179a6bf>] apic_timer_interrupt+0x6f/0x80
> [ 3992.191424]  <EOI>  [<ffffffff815ed233>] ? cpuidle_enter_state+0x73/0x2e0
> [ 3992.191432]  [<ffffffff815ed22e>] ? cpuidle_enter_state+0x6e/0x2e0
> [ 3992.191437]  [<ffffffff815ed567>] cpuidle_enter+0x17/0x20
> [ 3992.191441]  [<ffffffff810c0741>] cpu_startup_entry+0x3d1/0x4a0
> [ 3992.191445]  [<ffffffff81106fc6>] ? clockevents_config_and_register+0x26/0x30
> [ 3992.191448]  [<ffffffff81033c16>] start_secondary+0x1b6/0x260
>
> Fixes: b26b0d1e8b1 ("net: qdisc: use rcu prefix and silence sparse warnings")
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>


Acked-by: Cong Wang <cwang@...pensource.com>
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