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Date: Tue, 8 Sep 2015 17:34:56 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: "Wangnan (F)" <wangnan0@huawei.com>, acme@kernel.org, kan.liang@intel.com,
        linux-kernel@vger.kernel.org, lizefan@huawei.com, pi3orama@163.com,
        Adrian Hunter <adrian.hunter@intel.com>,
        Andi Kleen <ak@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf report: Fix invalid memory accessing
Message-ID: <20150908153456.GG2038@krava.brq.redhat.com>
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On Tue, Sep 08, 2015 at 12:18:13PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Sep 08, 2015 at 09:37:47AM +0200, Jiri Olsa escreveu:
> > On Mon, Sep 07, 2015 at 09:27:26PM +0800, Wangnan (F) wrote:
> > 
> > SNIP
> > 
> > > 
> > > I found the problem.
> > > 
> > > perf relies on build_cpu_topology() to fetch CPU_TOPOLOGY from sysfs. It
> > > depend on
> > > the existance of
> > > 
> > > /sys/devices/system/cpu/cpu%d/topology/core_siblings_list
> > > 
> > > However, CPU can be canceled by hotcpu subsystem. After that the directory
> > > of
> > > /sys/devices/system/cpu/cpu%d/topology is gone, which causes perf's
> > > write_cpu_topology() --> uild_cpu_topology() to fail, result in the above
> > > perf.data.
> > > 
> > > So I think my patch is required.
> > 
> > no question there.. I just meant it should be placed in
> > perf_event__preprocess_sample function with the rest of
> > the 'al' initialization, like in the patch below?
> > 
> > it does not compile, because there're many places calling
> > it and it'd need changing all callers to pass env, which
> > seems to require more changes..
> 
> Humm, I think that we can have a pointer to the current perf_env, be it
> from the current machine, or from the machine environment in the
> perf.data file in struct machine, that way we don't need to change that
> function prototype, I'm prototyping this now, will post a patch.

I was thinking of that.. but the perf_env is actualyl related to the
perf.data not to the current machine.. I think it should be part of
the session or perf_header

jirka