linux-kernel - ftrace_ops_list_func() triggered WARNING: at kernel/lockdep.c:3506

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Date:	Tue, 10 Jul 2012 23:47:35 +0800
From:	wfg@...ux.intel.com
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: ftrace_ops_list_func() triggered WARNING: at kernel/lockdep.c:3506

Hi Steven,

I can produce this in 3.5.0-rc6 as well as in 3.2.
Basically it's the rcu_dereference_raw(ftrace_ops_list) call that triggered the
__rcu_dereference_check()/lock_is_held()/check_flags() warning.

[    3.500806] Testing dynamic ftrace: PASSED
[    3.910268] Testing dynamic ftrace ops #1: (1 0 1 1 0) (1 1 2 1 0) (2 1 3 1 36) (2 2 4 1 164) [    4.000026] ------------[ cut here ]--
----------
[    4.000026] WARNING: at /c/wfg/linux/kernel/lockdep.c:3506 check_flags+0x140/0x177()
[    4.000026] Hardware name: Bochs

[    4.000026] Modules linked in:
[    4.000026] 
[    4.000026] Pid: 0, comm: swapper/0 Not tainted 3.5.0-rc6-bisect #48
[    4.000026] Call Trace:
[    4.000026]  <IRQ>  [<ffffffff81045250>] warn_slowpath_common+0x83/0x9c
[    4.000026]  [<ffffffff81045283>] warn_slowpath_null+0x1a/0x1c
[    4.000026]  [<ffffffff81099306>] check_flags+0x140/0x177
[    4.000026]  [<ffffffff8109a503>] lock_is_held+0x3c/0xa7
[    4.000026]  [<ffffffff81324901>] ? sub_preempt_count+0x7/0xe0
[    4.000026]  [<ffffffff8104e529>] ? __local_bh_enable+0xda/0x18f
[    4.000026]  [<ffffffff810d0a03>] ftrace_ops_list_func+0xae/0xf2
[    4.000026]  [<ffffffff81326d16>] ftrace_call+0x5/0x2b
[    4.000026]  [<ffffffff81324906>] ? sub_preempt_count+0xc/0xe0
[    4.000026]  [<ffffffff8104e529>] __local_bh_enable+0xda/0x18f
[    4.000026]  [<ffffffff8104e5f1>] _local_bh_enable+0x13/0x15
[    4.000026]  [<ffffffff8104ed7f>] irq_enter+0x4f/0x74
[    4.000026]  [<ffffffff81031ec9>] smp_apic_timer_interrupt+0x3e/0x98
[    4.000026]  [<ffffffff81327aef>] apic_timer_interrupt+0x6f/0x80
[    4.000026]  <EOI>  [<ffffffff810c4c85>] ? rcu_is_cpu_idle+0x67/0x78
[    4.000026]  [<ffffffff81038cc0>] ? native_safe_halt+0x6/0x8
[    4.000026]  [<ffffffff81099b2e>] ? trace_hardirqs_on+0xd/0xf
[    4.000026]  [<ffffffff8102215e>] default_idle+0x127/0x2cd
[    4.000026]  [<ffffffff810232a3>] cpu_idle+0x11d/0x1e7
[    4.000026]  [<ffffffff812fd3ac>] rest_init+0x130/0x137
[    4.000026]  [<ffffffff812fd27c>] ? csum_partial_copy_generic+0x16c/0x16c
[    4.000026]  [<ffffffff815a6baa>] start_kernel+0x3c8/0x3d5
[    4.000026]  [<ffffffff815a65ea>] ? repair_env_string+0x5a/0x5a
[    4.000026]  [<ffffffff815a62d6>] x86_64_start_reservations+0xb1/0xb5
[    4.000026]  [<ffffffff815a63d8>] x86_64_start_kernel+0xfe/0x10b

Thanks,
Fengguang

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