Re: [PATCH] perf report: Fix invalid memory accessing

["Wangnan (F)" <wangnan0@huawei.com>]

On 2015/9/7 21:03, Jiri Olsa wrote:
> On Mon, Sep 07, 2015 at 12:51:55PM +0000, Wang Nan wrote:
>> Commit e1e499aba570a2ea84d29822b7ea637ac41d9a51 (perf tools: Add
>> processor socket info to hist_entry and addr_location) reads env->cpu
>> array for each sample using index al.cpu. However, al.cpu can be -1 if
>> sample doesn't select PERF_SAMPLE_CPU. Also, env->cpu can be invalid if
>> feature CPU_TOPOLOGY not selected. We should validate env->cpu and al.cpu
>> before setting al.socket.
>>
>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
>> Cc: Kan Liang <kan.liang@intel.com>
>> Cc: Adrian Hunter <adrian.hunter@intel.com>
>> Cc: Andi Kleen <ak@linux.intel.com>
>> Cc: Jiri Olsa <jolsa@kernel.org>
>> Cc: Namhyung Kim <namhyung@kernel.org>
>> Cc: Stephane Eranian <eranian@google.com>
>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
>> ---
>>
>> Although theoretically CPU_TOPOLOGY feature should always be selected by
>> 'perf record', I did generate a perf.data without that feature. It has
>> header like this:
>>
>>   # perf report -i ./bad.perf.data  --header-only
>>   # ========
>>   # captured on: Thu Jan  8 09:30:15 2009
>>   # hostname : localhost
>>   # os release : 3.10.49-gd672fc4
>>   # perf version : 4.2.gc9df
>>   # arch : aarch64
>>   # nrcpus online : 8
>>   # nrcpus avail : 8
>>   # total memory : 1850768 kB
>>   # cmdline : /system/bin/perf record -e sync:sync_timeline -e kgsl:kgsl_register_event -g -a sleep 5
>>   # event : name = sync:sync_timeline, , id = { 1107, 1108, 1109, 1110, 1111, 1112 }, type = 2, size = 112, config = 0x3e7, { sample_period, sample_freq } = 1, sample_type = IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format = ID, disabled = 1, inherit = 1, mmap = 1, comm = 1, task = 1, sample_id_all = 1, exclude_guest = 1, mmap2 = 1, comm_exec = 1
>>   # event : name = kgsl:kgsl_register_event, , id = { 1113, 1114, 1115, 1116, 1117, 1118 }, type = 2, size = 112, config = 0x350, { sample_period, sample_freq } = 1, sample_type = IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format = ID, disabled = 1, inherit = 1, sample_id_all = 1, exclude_guest = 1
>>   # pmu mappings: cpu = 4, software = 1, tracepoint = 2
>>   # ========
>>   #
>>
>> It should be:
>>
>>   # ========
>>   # captured on: Thu Jan  8 11:26:41 2009
>>   ...
>>   # HEADER_CPU_TOPOLOGY info available, use -I to display
>>   # pmu mappings: cpu = 4, software = 1, tracepoint = 2
>>   # ========
>>
>> However, bad perf.data appears randomly. I can't stably reproduce it, so I
>> guess there might have another invalid memory accessing.
>>
>> ---
>>   tools/perf/builtin-report.c | 12 ++++++++++--
>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
>> index 4b43245..16d097d 100644
>> --- a/tools/perf/builtin-report.c
>> +++ b/tools/perf/builtin-report.c
>> @@ -158,8 +158,16 @@ static int process_sample_event(struct perf_tool *tool,
>>   		return -1;
>>   	}
>>   
>> -	/* read socket id from perf.data for perf report */
>> -	al.socket = env->cpu[al.cpu].socket_id;
>> +	/*
>> +	 * read socket id from perf.data for perf report
>> +	 * al.cpu is invalid if PERF_SAMPLE_CPU is not selected by this
>> +	 * sample.
>> +	 * env->cpu is invalid if CPU_TOPOLOGY feature is not set in
>> +	 * header.
>> +	 */
>> +	al.socket = -1;
>> +	if (env->cpu && al.cpu >= 0)
>> +		al.socket = env->cpu[al.cpu].socket_id;
> perf_event__preprocess_sample initializes al.socket from current system

No. For 'perf report' it initializes al.cpu from sample.


Commit message of e1e499aba570a2ea84d29822b7ea637ac41d9a51:

     Finor 'perf report', the socket id info is from perf.data.

     For others, the socket id info is from current system.

And at least checking of env->cpu is essential. I'm looking the problem 
I reported.
Looks like build_cpu_topology() is possible to fail.

Thank you.
> do we want to move this over there?
>
> also this change is just report specific, and we could need
> this in at least perf top
>
> jirka