linux-kernel - Re: [Bug 10489] Kprobe smoke test lockdep warning

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Date:	Mon, 21 Apr 2008 17:13:31 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Adrian Bunk" <bunk@...nel.org>
Cc:	ananth@...ibm.com, anil.s.keshavamurthy@...el.com,
	davem@...emloft.net, mhiramat@...hat.com,
	bugme-daemon@...zilla.kernel.org,
	"jean-marc LACROIX" <jeanmarc.lacroix@...e.fr>,
	linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...e.hu>,
	"Arjan van de Ven" <arjan@...ux.intel.com>
Subject: Re: [Bug 10489] Kprobe smoke test lockdep warning

On Mon, Apr 21, 2008 at 5:06 PM, Adrian Bunk <bunk@...nel.org> wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=10489
>
>  Please reply via email (more information from the submitter is in the
>  Bugzilla entry).
>
>
>  ReportedBy: jeanmarc.lacroix@...e.Fr
>
>  Earliest failing kernel version: 2.6.25
>  Distribution: DEbian Etch
>  Hardware Environment: PIII
>  Software Environment:
>  Problem Description: Warning at boot after running all
>  embedded test
>
>  Steps to reproduce: boot !!!
>
>
>    2.701005] Registering sys device '<NULL>'
>  [    2.702320] Registering sys device '<NULL>'
>  [    2.703711] Registering sys device '<NULL>'
>  [    2.704536] Initializing RT-Tester: OK
>  [    2.704824] device: 'snapshot': device_add
>  [    2.705140] PM: Adding info for No Bus:snapshot
>  [    2.706804] audit: initializing netlink socket (disabled)
>  [    2.707199] type=2000 audit(1208713807.707:1): initialized
>  [    2.707509] Kprobe smoke test started
>  [    2.709300] ------------[ cut here ]------------
>  [    2.709420] WARNING: at kernel/lockdep.c:2658 check_flags+0x4d/0x12c()
>  [    2.709541] Modules linked in:
>  [    2.709588] Pid: 1, comm: swapper Not tainted 2.6.25.jml.057 #1
>  [    2.709588]  [<c0126acc>] warn_on_slowpath+0x41/0x51
>  [    2.709588]  [<c010bafc>] ? save_stack_trace+0x1d/0x3b
>  [    2.709588]  [<c0140a83>] ? save_trace+0x37/0x89
>  [    2.709588]  [<c011987d>] ? kernel_map_pages+0x103/0x11c
>  [    2.709588]  [<c0109803>] ? native_sched_clock+0xca/0xea
>  [    2.709588]  [<c0142958>] ? mark_held_locks+0x41/0x5c
>  [    2.709588]  [<c0382580>] ? kprobe_exceptions_notify+0x322/0x3af
>  [    2.709588]  [<c0142aff>] ? trace_hardirqs_on+0xf1/0x119
>  [    2.709588]  [<c03825b3>] ? kprobe_exceptions_notify+0x355/0x3af
>  [    2.709588]  [<c0140823>] check_flags+0x4d/0x12c
>  [    2.709588]  [<c0143c9d>] lock_release+0x58/0x195
>  [    2.709588]  [<c038347c>] ? __atomic_notifier_call_chain+0x0/0x80
>  [    2.709588]  [<c03834d6>] __atomic_notifier_call_chain+0x5a/0x80
>  [    2.709588]  [<c0383508>] atomic_notifier_call_chain+0xc/0xe
>  [    2.709588]  [<c013b6d4>] notify_die+0x2d/0x2f
>  [    2.709588]  [<c038168a>] do_debug+0x67/0xfe
>  [    2.709588]  [<c0381287>] debug_stack_correct+0x27/0x30
>  [    2.709588]  [<c01564c0>] ? kprobe_target+0x1/0x34
>  [    2.709588]  [<c0156572>] ? init_test_probes+0x50/0x186
>  [    2.709588]  [<c04fae48>] init_kprobes+0x85/0x8c
>  [    2.709588]  [<c04e947b>] kernel_init+0x13d/0x298
>  [    2.709588]  [<c04e933e>] ? kernel_init+0x0/0x298
>  [    2.709588]  [<c04e933e>] ? kernel_init+0x0/0x298
>  [    2.709588]  [<c0105ef7>] kernel_thread_helper+0x7/0x10
>  [    2.709588]  =======================
>  [    2.709588] ---[ end trace 778e504de7e3b1e3 ]---
>  [    2.709588] possible reason: unannotated irqs-off.
>  [    2.709588] irq event stamp: 370065
>  [    2.709588] hardirqs last  enabled at (370065): [<c0382580>]
>  kprobe_exceptions_notify+0x322/0x3af
>  [    2.709588] hardirqs last disabled at (370064): [<c0381bb7>]
>  do_int3+0x1d/0x7d
>  [    2.709588] softirqs last  enabled at (370050): [<c012b464>]
>  __do_softirq+0xfa/0x100
>  [    2.709588] softirqs last disabled at (370045): [<c0107438>]
>  do_softirq+0x74/0xd9
>  [    2.714751] Kprobe smoke test passed successfully
>  [    2.716150] Total HugeTLB memory allocated, 0
>  [    2.717288] VFS: Disk quotas dquot_6.5.1
>  [    2.717689] Dquot-cache hash table entries: 1024 (order 0, 4096 bytes)
>  [    2.719630] device class 'bsg': registering
>  [    2.720568] Block layer SCSI generic (bsg) driver version 0.4 loaded (major
>  253)
>  [    2.720619] io scheduler noop registered
>  [    2.720732] io scheduler anticipatory registered
>  [    2.720848] io scheduler deadline registered
>  [    2.721089] io scheduler cfq registered (default)
>  [    2.721354] pci 0000:00:01.0: Boot video device
>

This is because kprobes (just like kmemcheck and mmiotrace) needs to
disable interrupts while it single-steps the instruction. This is not
dangerous, and should be fixed by doing as the warning suggests, by
annotating the irqs-off. I don't remember the name of the function(s),
it is probably somewhere in lockdep.h.

Vegard


-- 
"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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