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Subject: Re: [PATCH v1 10/11] perf intel-pt: Smatch: Fix potential NULL
 pointer dereference
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Andi Kleen <ak@linux.intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Jin Yao <yao.jin@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
        Alexios Zavras <alexios.zavras@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Changbin Du <changbin.du@intel.com>,
        Eric Saint-Etienne <eric.saint.etienne@oracle.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Thomas Richter <tmricht@linux.ibm.com>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20190702103420.27540-1-leo.yan@linaro.org>
 <20190702103420.27540-11-leo.yan@linaro.org>
 <cfef1777-141e-4223-e0c1-1a3f3aee1d3c@intel.com>
 <20190703013553.GB6852@leoy-ThinkPad-X240s>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
Message-ID: <b65cf4c6-3484-85c8-d191-35021ed6ed3e@intel.com>
Date:   Wed, 3 Jul 2019 08:19:19 +0300
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On 3/07/19 4:35 AM, Leo Yan wrote:
> Hi Adrian,
> 
> On Tue, Jul 02, 2019 at 02:07:40PM +0300, Adrian Hunter wrote:
>> On 2/07/19 1:34 PM, Leo Yan wrote:
>>> Based on the following report from Smatch, fix the potential
>>> NULL pointer dereference check.
>>
>> It never is NULL.  Remove the NULL test if you want:
>>
>> -	if (session->itrace_synth_opts && session->itrace_synth_opts->set) {
>> +	if (session->itrace_synth_opts->set) {
>>
>> But blindly making changes like below is questionable.
> 
> Thanks for suggestions.
> 
> I checked report and script commands, as you said, both command will
> always set session->itrace_synth_opts.  For these two commands, we can
> safely remove the NULL test.
> 
> Because perf tool contains many sub commands, so I don't have much
> confidence it's very safe to remove the NULL test for all cases; e.g.
> there have cases which will process aux trace buffer but without
> itrace options; for this case, session->itrace_synth_opts might be NULL.
> 
> For either way (remove NULL test or keep NULL test), I don't want to
> introduce regression and extra efforts by my patch.  So want to double
> confirm with you for this :)

Yes, intel_pt_process_auxtrace_info() only gets called if a tool sets up the
tools->auxtrace_info() callback.  The tools that do that also set
session->itrace_synth_opts.