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

[Wangnan (F)]

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@xxxxxxxxxx>
> > Cc: Kan Liang <kan.liang@xxxxxxxxx>
> > Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> > Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > ---
> >
> > 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


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