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From: Ingo Molnar <mingo@elte.hu>
To: Cyrill Gorcunov <gorcunov@openvz.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: maciej.rutecki@gmail.com, Shaun Ruffell <sruffell@digium.com>,
	Don Zickus <dzickus@redhat.com>,
	linux-kernel@vger.kernel.org, Lin Ming <ming.m.lin@intel.com>
Subject: Re: [regression 2.6.39-rc2][bisected] "perf, x86: P4 PMU - Read proper MSR register to catch" and NMIs
Date: Thu, 14 Apr 2011 08:47:37 +0200	[thread overview]
Message-ID: <20110414064737.GB15535@elte.hu> (raw)
In-Reply-To: <4DA6011F.7070405@openvz.org>


* Cyrill Gorcunov <gorcunov@openvz.org> wrote:

> -	apic_write(APIC_LVTPC, APIC_DM_NMI);
> 
>  	handled = x86_pmu.handle_irq(args->regs);
>  	if (!handled)
>  		return NOTIFY_DONE;
> 
> +	/*
> +	 * Unmasking should be done after IRQ handled, otherwise
> +	 * there is a race between clearing of counter overflow
> +	 * flag and LTV entry unmasking (which might lead to double
> +	 * NMIs generation).
> +	 */
> +	apic_write(APIC_LVTPC, APIC_DM_NMI);

Here we could leak a masked IRQ through the !handled path. If we got a LVTPC 
irq we better handle it and unmask the LVTPC unconditionally - regardless of 
whether we consider it 'handled' or not from the kernel POV ...

Thanks,

	Ingo

  parent reply	other threads:[~2011-04-14  6:47 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-06 22:30 Shaun Ruffell
2011-04-07  0:16 ` Don Zickus
2011-04-07  3:18   ` Cyrill Gorcunov
2011-04-07 14:38     ` Shaun Ruffell
2011-04-07 14:43       ` Cyrill Gorcunov
2011-04-13 19:33 ` Maciej Rutecki
2011-04-13 20:01   ` Cyrill Gorcunov
2011-04-13 20:35     ` Shaun Ruffell
2011-04-13 20:43       ` Cyrill Gorcunov
2011-04-13 21:22         ` Don Zickus
2011-04-13 21:25           ` Cyrill Gorcunov
2011-04-13 21:53             ` Shaun Ruffell
2011-04-14 14:30               ` Shaun Ruffell
2011-04-14 14:33                 ` Cyrill Gorcunov
2011-04-14  6:47     ` Ingo Molnar [this message]
2011-04-14  7:51       ` Cyrill Gorcunov
2011-04-14  8:05         ` Ingo Molnar
2011-04-14  9:27           ` Cyrill Gorcunov

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