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    SubjectRe: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages
    On 05.06.2011 16:10, Ingo Molnar wrote:
    >
    > * 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()?

    (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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