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Date: Sun, 5 Jun 2011 16:10:03 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Arne Jansen <lists@die-jansens.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>, mingo@redhat.com,
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Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages
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* Arne Jansen <lists@die-jansens.de> wrote:

> Here we go:
> 
> http://eischnee.de/lockup.txt
> 
> Now it's your turn :)

So the lockup is in:

 [<ffffffff813af2d9>] do_raw_spin_lock+0x129/0x170
 [<ffffffff8108a4bd>] ? try_to_wake_up+0x29d/0x350
 [<ffffffff8185ce71>] _raw_spin_lock+0x51/0x70
 [<ffffffff81092df6>] ? vprintk+0x76/0x4a0
 [<ffffffff81092df6>] vprintk+0x76/0x4a0
 [<ffffffff810c5f8d>] ? trace_hardirqs_off+0xd/0x10
 [<ffffffff8108a4bd>] ? try_to_wake_up+0x29d/0x350
 [<ffffffff81859e19>] printk+0x63/0x65
 [<ffffffff8108a4bd>] ? try_to_wake_up+0x29d/0x350
 [<ffffffff81091f98>] warn_slowpath_common+0x38/0xb0
 [<ffffffff81092025>] warn_slowpath_null+0x15/0x20
 [<ffffffff8108a4bd>] try_to_wake_up+0x29d/0x350
 [<ffffffff8108a5a0>] wake_up_process+0x10/0x20
 [<ffffffff8185c071>] __up+0x41/0x50
 [<ffffffff810b937c>] up+0x3c/0x50
 [<ffffffff81092a36>] console_unlock+0x1a6/0x200
 [<ffffffff81092f86>] vprintk+0x206/0x4a0
 [<ffffffff810c5f8d>] ? trace_hardirqs_off+0xd/0x10
 [<ffffffff810ba6db>] ? local_clock+0x4b/0x60
 [<ffffffffa0012000>] ? 0xffffffffa0011fff
 [<ffffffff81859e19>] printk+0x63/0x65
 [<ffffffffa001201d>] test_init+0x1d/0x2b [test]
 [<ffffffff810001ce>] do_one_initcall+0x3e/0x170

Somehow we end up generating a WARN_ON() within a printk()'s 
try_to_wake_up() and predictably we lock up on that ...

Peter?

Arne, mind helping a bit with:

 [<ffffffff81091f98>] warn_slowpath_common+0x38/0xb0
 [<ffffffff81092025>] warn_slowpath_null+0x15/0x20
 [<ffffffff8108a4bd>] try_to_wake_up+0x29d/0x350

which WARN_ON() does that correspond to in try_to_wake_up()?

Thanks,

	Ingo
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