linux-kernel - Re: [PATCH] x86 MCE: shut up lockdep warning

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Date:	Fri, 8 May 2009 11:10:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86 MCE: shut up lockdep warning


* Andi Kleen <andi@...stfloor.org> wrote:

> On Fri, May 08, 2009 at 11:47:09AM +0800, Shaohua Li wrote:
> > lockdep report below warning when I try to offline one cpu:
> > [  110.835487] =================================
> > [  110.835616] [ INFO: inconsistent lock state ]
> > [  110.835688] 2.6.30-rc4-00336-g8c9ed89 #52
> > [  110.835757] ---------------------------------
> > [  110.835828] inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> > [  110.835908] swapper/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
> > [  110.835982]  (cmci_discover_lock){?.+...}, at: [<ffffffff80236dc0>] cmci_clear+0x30/0x9b
> > 
> > smp_call_function_single() will disable interrupt. moving mce reenable/disable
> > to workqueue, so no irq is disabled.
> 
> Looks good. Thanks.
> 
> Acked-by: Andi Kleen <ak@...ux.intel.com>

The report is useful, but the fix does not look good at all, and you 
should never have acked it:

 - it works around a lockdep warning

 - you did not realize the real bug while the warning was plain

 - plus the patch introduces a fragile (because complex)
   work_on_cpu() call into the CPU hotplug path, which could have 
   caused followup regressions.

Please also Cc: the relevant upstream subsystem maintainers in such 
cases (the x86 maintaiers in this case).

Thanks,

	Ingo
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