linux-kernel - Re: suspicious RCU usage in copy

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Date:	Sat, 11 Aug 2012 11:02:28 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	linux-kernel@...r.kernel.org
Subject: Re: suspicious RCU usage in copy_namespaces()

Fengguang Wu <fengguang.wu@...el.com> writes:

> Hi Eric,
>
> The below warning shows up since commit

Thanks. I am believe the usage is actually correct but I will dig some
more and see what it takes to convince the tools of that.

Eric


>
> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git userns-always-map-user-v45
> head:   38a0b1b84f5f613ff4e01fffda27f87d4cb2b649
> commit: 928ccdb582292cec4552bbf5831f7d374ff60269  userns: Allow unprivileged users to create new namespaces
>
> [    0.053560] ===============================
> [    0.054000] [ INFO: suspicious RCU usage. ]
> [    0.055001] 3.6.0-rc1-00116-g48de0c9 #176 Not tainted
> [    0.055999] -------------------------------
> [    0.057001] /c/kernel-tests/src/linux/kernel/nsproxy.c:126 suspicious rcu_dereference_check() usage!
> [    0.057999] 
> [    0.057999] other info that might help us debug this:
> [    0.057999] 
> [    0.058999] 
> [    0.058999] rcu_scheduler_active = 1, debug_locks = 1
> [    0.059998] no locks held by swapper/0.
> [    0.060998] 
> [    0.060998] stack backtrace:
> [    0.061999] Pid: 0, comm: swapper Not tainted 3.6.0-rc1-00116-g48de0c9 #176
> [    0.062999] Call Trace:
> [    0.063532]  [<b1047586>] lockdep_rcu_suspicious+0xba/0xc3
> [    0.064004]  [<b103218e>] copy_namespaces+0x59/0x1fd
> [    0.066002]  [<b101792b>] copy_process.part.49+0xec6/0xf02
> [    0.067002]  [<b1011f51>] ? kvm_clock_read+0x18/0x26
> [    0.068004]  [<b1488949>] ? start_kernel+0x304/0x304
> [    0.069000]  [<b1017a49>] do_fork+0xc6/0x23d
> [    0.070000]  [<b104698b>] ? trace_hardirqs_off+0xb/0xd
> [    0.071001]  [<b1037fc0>] ? local_clock+0x36/0x4e
> [    0.072003]  [<b120ab99>] ? _raw_spin_unlock_irqrestore+0x39/0x4f
> [    0.073053]  [<b1488949>] ? start_kernel+0x304/0x304
> [    0.074002]  [<b1006826>] kernel_thread+0x72/0x7a
> [    0.074999]  [<b1488949>] ? start_kernel+0x304/0x304
> [    0.076001]  [<b120fc5c>] ? common_interrupt+0x3c/0x3c
> [    0.077000]  [<b11fc816>] rest_init+0x1a/0x112
> [    0.077999]  [<b1488944>] start_kernel+0x2ff/0x304
> [    0.079000]  [<b14882c2>] i386_start_kernel+0x78/0x7d
> [    0.080376] Performance Events: unsupported Netburst CPU model 6 no PMU driver, software events only.
> [    0.086440] device: 'platform': device_add
>
> Thanks,
> Fengguang
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