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SubjectRe: suspicious RCU usage in copy_namespaces()
Fengguang Wu <fengguang.wu@intel.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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