linux-kernel - Re: [PATCH] perf/x86/intel: Add cpu_(prepare|starting|dying) for core

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Message-ID: <20150421105239.GA26455@gmail.com>
Date:	Tue, 21 Apr 2015 12:52:40 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf/x86/intel: Add cpu_(prepare|starting|dying) for
 core_pmu


* Jiri Olsa <jolsa@...nel.org> wrote:

> The core_pmu does not define cpu_* callbacks, which handles
> allocation of 'struct cpu_hw_events::shared_regs' data,
> initialization of debug store and PMU_FL_EXCL_CNTRS counters.
> 
> While this probably won't happen on bare metal, virtual CPU can
> define x86_pmu.extra_regs together with PMU version 1 and thus
> be using core_pmu -> using shared_regs data without it being
> allocated. That could could leave to following panic:
> 
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: [<ffffffff8152cd4f>] _spin_lock_irqsave+0x1f/0x40

ok.

> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> index 9da2400c2ec3..0a61a9a021de 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -2533,6 +2533,10 @@ ssize_t intel_event_sysfs_show(char *page, u64 config)
>  	return x86_event_sysfs_show(page, config, event);
>  }
>  
> +static int  intel_pmu_cpu_prepare(int cpu);
> +static void intel_pmu_cpu_starting(int cpu);
> +static void intel_pmu_cpu_dying(int cpu);
> +
>  static __initconst const struct x86_pmu core_pmu = {
>  	.name			= "core",
>  	.handle_irq		= x86_pmu_handle_irq,
> @@ -2559,6 +2563,9 @@ static __initconst const struct x86_pmu core_pmu = {
>  	.guest_get_msrs		= core_guest_get_msrs,
>  	.format_attrs		= intel_arch_formats_attr,
>  	.events_sysfs_show	= intel_event_sysfs_show,
> +	.cpu_prepare		= intel_pmu_cpu_prepare,
> +	.cpu_starting		= intel_pmu_cpu_starting,
> +	.cpu_dying		= intel_pmu_cpu_dying,
>  };

Instead of adding prototype declarations, please arrange the x86_pmu 
definition's position so that it comes after the required functions - 
so that no prototypes are needed.

Thanks,

	Ingo
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