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

[Arne Jansen]

On 05.06.2011 16:10, Ingo Molnar wrote:
> * 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()?

(gdb) info line *0xffffffff8108a4bd
Line 934 of "kernel/sched.c" starts at address 0xffffffff8108a498 
<try_to_wake_up+632> and ends at 0xffffffff8108a4c8 <try_to_wake_up+680>.

sched.c:934: in function __task_rq_lock
        lockdep_assert_held(&p->pi_lock);

I'm currently testing on commit 0122ec5b02f766c355b3168d.

-Arne

> Thanks,
>
> 	Ingo
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