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Subjectv2.6.27-rc4: lockdep warning in ftrace

Some very superficial searching of lkml didn't reveal existing reports
of this problem, so I report anyway. Please accept my apologies if
this has been reported, discussed, fixed, etc. already. Here goes:

calling rcu_torture_init+0x0/0x680
rcu-torture:--- Start of test: nreaders=4 nfakewriters=4
stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval=3
stutter=5 irqreader=1
initcall rcu_torture_init+0x0/0x680 returned 0 after 13 msecs
calling rcupreempt_trace_init+0x0/0x120
initcall rcupreempt_trace_init+0x0/0x120 returned 0 after 0 msecs
calling utsname_sysctl_init+0x0/0x20
initcall utsname_sysctl_init+0x0/0x20 returned 0 after 0 msecs
calling init_sched_switch_trace+0x0/0x40
Testing tracer sched_switch: PASSED
initcall init_sched_switch_trace+0x0/0x40 returned 0 after 217 msecs
calling init_stack_trace+0x0/0x10
Testing tracer sysprof: PASSED
initcall init_stack_trace+0x0/0x10 returned 0 after 104 msecs
calling init_function_trace+0x0/0x10
Testing tracer ftrace: PASSED
Testing dynamic ftrace: PASSED
initcall init_function_trace+0x0/0x10 returned 0 after 563 msecs
calling init_irqsoff_tracer+0x0/0x30
Testing tracer irqsoff: PASSED
Testing tracer preemptoff: PASSED
Testing tracer preemptirqsoff: <4>------------[ cut here ]------------
WARNING: at /uio/arkimedes/s29/vegardno/git-working/linux-2.6/kernel/lockdep.c:2884
Pid: 261, comm: rcu_torture_wri Not tainted 2.6.27-rc4-00131-g83097ac-dirty #53
[<c013d8a4>] warn_on_slowpath+0x54/0x80
[<c015fd4b>] ? trace_hardirqs_off+0xb/0x10
[<c010b615>] ? native_sched_clock+0xb5/0x110
[<c015788c>] ? sched_clock_cpu+0xdc/0x170
[<c015fd4b>] ? trace_hardirqs_off+0xb/0x10
[<c01579ff>] ? cpu_clock+0x4f/0x80
[<c018fb48>] ? ftrace_now+0x8/0x10
[<c01423f4>] ? __local_bh_disable+0x44/0xa0
[<c0142460>] ? local_bh_disable+0x10/0x20
[<c01423f4>] ? __local_bh_disable+0x44/0xa0
[<c0192606>] ? trace_preempt_off+0xc6/0xf0
[<c015f17c>] check_flags+0x13c/0x160
[<c0142460>] ? local_bh_disable+0x10/0x20
[<c0164683>] lock_acquire+0x43/0xc0
[<c01375f2>] ? add_preempt_count+0x52/0xd0
[<c01862f0>] ? rcu_torture_writer+0x0/0x180
[<c05d54ea>] _spin_lock_bh+0x4a/0x80
[<c018635f>] ? rcu_torture_writer+0x6f/0x180
[<c018635f>] rcu_torture_writer+0x6f/0x180
[<c01519c7>] kthread+0x47/0x80
[<c0151980>] ? kthread+0x0/0x80
[<c0105da3>] kernel_thread_helper+0x7/0x10
---[ end trace a7919e7f17c0a725 ]---
possible reason: unannotated irqs-on.
irq event stamp: 2719
hardirqs last enabled at (2717): [<c01626eb>] trace_hardirqs_on+0xb/0x10
hardirqs last disabled at (2718): [<c015fd4b>] trace_hardirqs_off+0xb/0x10
softirqs last enabled at (2688): [<c018638d>] rcu_torture_writer+0x9d/0x180
softirqs last disabled at (2719): [<c05d54b4>] _spin_lock_bh+0x14/0x80
initcall init_irqsoff_tracer+0x0/0x30 returned 0 after 362 msecs
calling init_wakeup_tracer+0x0/0x10
Testing tracer wakeup: PASSED
initcall init_wakeup_tracer+0x0/0x10 returned 0 after 333 msecs
calling init_mmio_trace+0x0/0x10
initcall init_mmio_trace+0x0/0x10 returned 0 after 0 msecs


"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036

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