Re: [debug patch] printk: Add a printk killswitch to robustify NMIwatchdog messages

From: Ingo Molnar
Date: Sun Jun 05 2011 - 10:10:27 EST



* Arne Jansen <lists@xxxxxxxxxxxxxx> 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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