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Date: Fri, 12 Mar 2010 00:31:28 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, Lin Ming <ming.m.lin@intel.com>,
       "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Stephane Eranian <eranian@google.com>,
       Robert Richter <robert.richter@amd.com>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] x86,perf: Implement minimal P4 PMU driver v14
Message-ID: <20100311213128.GE25162@lenovo>
References: <20100310183102.GC8070@lenovo> <1268274775.4996.16.camel@minggr.sh.intel.com> <20100311165439.GB5129@lenovo> <20100311181646.GA12235@elte.hu> <20100311183921.GA30249@elte.hu> <20100311211538.GC25162@lenovo> <1268342662.5037.143.camel@laptop>
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On Thu, Mar 11, 2010 at 10:24:22PM +0100, Peter Zijlstra wrote:
> On Fri, 2010-03-12 at 00:15 +0300, Cyrill Gorcunov wrote:
> 
> > Perhaps something like the patch below (tested with kvm)? With this patch
> > we will actually waste ~4/8 bytes per PMU (intel,amd,p6) since this call
> > hits on p4 only, so I think perhaps better to use one x86 scheduler hook
> > instead of empty schedule_events() in PMU, hmm?
> > ---
> > 
> > x86,perf: Fix NULL deref on not assigned x86_pmu
> > 
> > In case of not assigned x86_pmu and software events
> > NULL dereference may being hit via x86_pmu::schedule_events
> > method.
> > 
> > Fix it by calling x86_pmu::schedule_events only if we
> > have one. Otherwise use general scheduler.
> > 
> > Also the former x86_schedule_events calls restored.
> 
> Hrm,.. not sure that makes sense, sure it might not crash anymore, but
> its not making much sense to compute anything if we don't have an
> initialized x86_pmu.
> 
> Doesn't adding something like:
> 
>   if (!x86_pmu_initialized())
>    return;
> 
> to hw_perf_group_sched_in() make more sense? We seem to do that for all
> these weak things except this one.
> 

As far as I see it'll not update tstamp_running then (in x86_event_sched_in).
Or I miss somethig?

	-- Cyrill