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SubjectRe: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

* Arne Jansen <lists@die-jansens.de> wrote:

> >>>With the all-locks-printed output we can double check what locks are
> >>>held.
>
> btw, the output posted earlier also contains some BUG: spinlock
> lockup.

hm, it's hard to interpret that without the spin_lock()/unlock()
logic keeping the dumps apart.

Was lockdep enabled as you started the test?

but ... if the lock is reasonably sorted then it's this one:

<0>BUG: spinlock lockup on CPU#3, modprobe/22211, ffffffff81e1c0c0
Pid: 22211, comm: modprobe Tainted: G W 2.6.39-rc3+ #19
Call Trace:
[<ffffffff813af306>] do_raw_spin_lock+0x156/0x170
[<ffffffff8185ce71>] _raw_spin_lock+0x51/0x70
[<ffffffff81092df6>] ? vprintk+0x76/0x4a0
[<ffffffff81092df6>] vprintk+0x76/0x4a0
[<ffffffff810c5f8d>] ? trace_hardirqs_off+0xd/0x10
[<ffffffff81859e19>] printk+0x63/0x65
[<ffffffff813af301>] do_raw_spin_lock+0x151/0x170
[<ffffffff8108a4bd>] ? try_to_wake_up+0x29d/0x350
[<ffffffff8185ce71>] _raw_spin_lock+0x51/0x70
[<ffffffff81092df6>] ? vprintk+0x76/0x4a0
[<ffffffff81092df6>] vprintk+0x76/0x4a0
[<ffffffff8108758b>] ? cpuacct_charge+0x9b/0xb0
[<ffffffff8108750f>] ? cpuacct_charge+0x1f/0xb0
[<ffffffff8108a4bd>] ? try_to_wake_up+0x29d/0x350
[<ffffffff81859e19>] printk+0x63/0x65
[<ffffffff813af090>] spin_bug+0x70/0xf0
[<ffffffff813af2d9>] do_raw_spin_lock+0x129/0x170
[<ffffffff8108a4bd>] ? try_to_wake_up+0x29d/0x350
[<ffffffff8185ce71>] _raw_spin_lock+0x51/0x70
[<ffffffff81092df6>] ? vprintk+0x76/0x4a0

and it occured before the lockup in the scheduler.

Which could be due to a race between disabling lockdep on one CPU and
the scheduler doing the lock-held check on another CPU.

Do you get any messages after the assert is removed, during the test?

Thanks,

Ingo


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