linux-kernel - Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

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Message-ID: <20110605172052.GA1036@elte.hu>
Date:	Sun, 5 Jun 2011 19:20:52 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arne Jansen <lists@...-jansens.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
	frank.rowand@...sony.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages


* Arne Jansen <lists@...-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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