linux-kernel - Re: new (common) WARNING message?

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Message-ID: <49707398.1040102@s5r6.in-berlin.de>
Date:	Fri, 16 Jan 2009 12:46:32 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Mike Travis <travis@....com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: new (common) WARNING message?

Mike Travis wrote:
> I've been seeing these on and off for a while now.  They don't
> seem to affect anything but perhaps I should track them down?
> 
> Do you know what it means?  (I'm asking you because evidently
> debugobjects.c is from you?  I read the good explanation in the
> changelog of 3ac7fe5a, but it didn't clue me into what's going
> on. ;-)
> 
> Thanks,
> Mike
> --
> 
> [ 1294.973592] ODEBUG: object is on stack, but not annotated
> [ 1294.974067] ------------[ cut here ]------------
> [ 1294.974067] WARNING: at /mdata/lwork/polaris3/travis/workareas/ingo-latest/linux-2.6-for-ingo/lib/debugobjects.c:253 __debug_object_init+0x27c/0x2f0()
> [ 1294.974067] Hardware name: X7DBT
> [ 1294.974067] Pid: 4150, comm: offline-test Tainted: G        W  2.6.29-rc1-4k-defconfig.01151634-00255-gc99dbbe-dirty #89
> [ 1294.974067] Call Trace:
> [ 1294.974067]  [<ffffffff81047e3f>] warn_slowpath+0xd3/0xf2
> [ 1294.974067]  [<ffffffff8106c64f>] ? trace_hardirqs_off+0xd/0xf
> [ 1294.974067]  [<ffffffff815ca6ac>] ? _spin_unlock_irqrestore+0x3d/0x4c
> [ 1294.974067]  [<ffffffff8125bebe>] ? __debug_check_no_obj_freed+0xf6/0x14c
> [ 1294.974067]  [<ffffffff81048d3c>] ? printk+0x6c/0x6e
> [ 1294.974067]  [<ffffffff8125c449>] ? __debug_object_init+0xf9/0x2f0
> [ 1294.974067]  [<ffffffff8125b3ae>] ? _raw_spin_unlock+0xc7/0xf6
> [ 1294.974067]  [<ffffffff8125c5cc>] __debug_object_init+0x27c/0x2f0
> [ 1294.974067]  [<ffffffff8125c66d>] debug_object_init+0x14/0x17
> [ 1294.974067]  [<ffffffff81052320>] init_timer+0x1d/0x2a
> [ 1294.974067]  [<ffffffff81025077>] hpet_cpuhp_notify+0xad/0x124
> [ 1294.974067]  [<ffffffff81025233>] ? hpet_work+0x0/0x21a
> [ 1294.974067]  [<ffffffff81062057>] notifier_call_chain+0x33/0x5b
> [ 1294.974067]  [<ffffffff810620ad>] __raw_notifier_call_chain+0xe/0x10
> [ 1294.974067]  [<ffffffff810620c3>] raw_notifier_call_chain+0x14/0x16
> [ 1294.974067]  [<ffffffff815c5190>] _cpu_up+0x115/0x155
> [ 1294.974067]  [<ffffffff815c527c>] cpu_up+0x65/0x73
> [ 1294.974067]  [<ffffffff815ac21d>] store_online+0x52/0x7b
> [ 1294.974067]  [<ffffffff812ff775>] sysdev_store+0x20/0x22
> [ 1294.974067]  [<ffffffff81134f6b>] sysfs_write_file+0xe9/0x11e
> [ 1294.974067]  [<ffffffff810e0da5>] vfs_write+0xea/0x148
> [ 1294.974067]  [<ffffffff810e0ec7>] sys_write+0x4c/0x72
> [ 1294.974067]  [<ffffffff8100c6cb>] system_call_fastpath+0x16/0x1b
> [ 1294.974067] ---[ end trace 4eaa2a86a8e2da24 ]---
> --

The warning tells us that arch/x86/kernel/hpet.c::hpet_cpuhp_notify()
allocates a timer on the stack.  In particular, it allocates a struct
hpet_work_struct on the stack which incorporates a timer.

Now, a timer instance on a stack would be wrong if the function which
defined that timer exits too early.  But in case of hpet_cpuhp_notify(),
this is OK since
  - it waits for the work be done,
  - the work does not rearm itself.
IOW the work and thus the timer won't be accessed anymore when
hpet_cpuhp_notify() returns.

So, hpet_cpuhp_notify() apparently needs a variant of INIT_DELAYED_WORK
which uses init_timer_on_stack instead of init_timer, to say "trust me,
I know what I'm doing".
-- 
Stefan Richter
-=====-==--= ---= =----
http://arcgraph.de/sr/
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