Re: [PATCH v3] perf record: Fix segfault with --overwrite and --max-size

[Namhyung Kim]

Hello,

On Sun, Feb 5, 2023 at 5:29 PM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote:
>
> Hello,
>
> Ping again, please take time to review, thanks.

Sorry for the late reply.  Now it looks good to me.

>
>
> Thanks,
> Yang
>
>
> On 2023/1/28 9:27, Yang Jihong wrote:
> > Hello,
> >
> > The data written by the thread (data.X file) has been saved as
> > recommended in v2 patch. Please check whether it is feasible. Thank you.
> >
> > Thanks,
> > Yang
> >
> > On 2023/1/13 15:38, Yang Jihong wrote:
> >> When --overwrite and --max-size options of perf record are used together,
> >> a segmentation fault occurs. The following is an example:
> >>
> >>    # perf record -e sched:sched* --overwrite --max-size 1K -a -- sleep 1
> >>    [ perf record: Woken up 1 times to write data ]
> >>    perf: Segmentation fault
> >>    Obtained 12 stack frames.
> >>    ./perf/perf(+0x197673) [0x55f99710b673]
> >>    /lib/x86_64-linux-gnu/libc.so.6(+0x3ef0f) [0x7fa45f3cff0f]
> >>    ./perf/perf(+0x8eb40) [0x55f997002b40]
> >>    ./perf/perf(+0x1f6882) [0x55f99716a882]
> >>    ./perf/perf(+0x794c2) [0x55f996fed4c2]
> >>    ./perf/perf(+0x7b7c7) [0x55f996fef7c7]
> >>    ./perf/perf(+0x9074b) [0x55f99700474b]
> >>    ./perf/perf(+0x12e23c) [0x55f9970a223c]
> >>    ./perf/perf(+0x12e54a) [0x55f9970a254a]
> >>    ./perf/perf(+0x7db60) [0x55f996ff1b60]
> >>    /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe6)
> >> [0x7fa45f3b2c86]
> >>    ./perf/perf(+0x7dfe9) [0x55f996ff1fe9]
> >>    Segmentation fault (core dumped)
> >>
> >> backtrace of the core file is as follows:
> >>
> >>    (gdb) bt
> >>    #0  record__bytes_written (rec=0x55f99755a200 <record>) at
> >> builtin-record.c:234
> >>    #1  record__output_max_size_exceeded (rec=0x55f99755a200 <record>)
> >> at builtin-record.c:242
> >>    #2  record__write (map=0x0, size=12816, bf=0x55f9978da2e0,
> >> rec=0x55f99755a200 <record>) at builtin-record.c:263
> >>    #3  process_synthesized_event (tool=tool@entry=0x55f99755a200
> >> <record>, event=event@entry=0x55f9978da2e0, sample=sample@entry=0x0,
> >> machine=machine@entry=0x55f997893658) at builtin-record.c:618
> >>    #4  0x000055f99716a883 in __perf_event__synthesize_id_index
> >> (tool=tool@entry=0x55f99755a200 <record>,
> >> process=process@entry=0x55f997002aa0 <process_synthesized_event>,
> >> evlist=0x55f9978928b0, machine=machine@entry=0x55f997893658,
> >>        from=from@entry=0) at util/synthetic-events.c:1895
> >>    #5  0x000055f99716a91f in perf_event__synthesize_id_index
> >> (tool=tool@entry=0x55f99755a200 <record>,
> >> process=process@entry=0x55f997002aa0 <process_synthesized_event>,
> >> evlist=<optimized out>, machine=machine@entry=0x55f997893658)
> >>        at util/synthetic-events.c:1905
> >>    #6  0x000055f996fed4c3 in record__synthesize (tail=tail@entry=true,
> >> rec=0x55f99755a200 <record>) at builtin-record.c:1997
> >>    #7  0x000055f996fef7c8 in __cmd_record (argc=argc@entry=2,
> >> argv=argv@entry=0x7ffc67551260, rec=0x55f99755a200 <record>) at
> >> builtin-record.c:2802
> >>    #8  0x000055f99700474c in cmd_record (argc=<optimized out>,
> >> argv=0x7ffc67551260) at builtin-record.c:4258
> >>    #9  0x000055f9970a223d in run_builtin (p=0x55f997564d88
> >> <commands+264>, argc=10, argv=0x7ffc67551260) at perf.c:330
> >>    #10 0x000055f9970a254b in handle_internal_command (argc=10,
> >> argv=0x7ffc67551260) at perf.c:384
> >>    #11 0x000055f996ff1b61 in run_argv (argcp=<synthetic pointer>,
> >> argv=<synthetic pointer>) at perf.c:428
> >>    #12 main (argc=<optimized out>, argv=0x7ffc67551260) at perf.c:562
> >>
> >> The reason is that record__bytes_written accesses the freed memory
> >> rec->thread_data,
> >> The process is as follows:
> >>    __cmd_record
> >>      -> record__free_thread_data
> >>        -> zfree(&rec->thread_data)         // free rec->thread_data
> >>      -> record__synthesize
> >>        -> perf_event__synthesize_id_index
> >>          -> process_synthesized_event
> >>            -> record__write
> >>              -> record__bytes_written      // access rec->thread_data
> >>
> >> We add a member variable "thread_bytes_written" in the struct "record"
> >> to save the data size written by the threads.
> >>
> >> Fixes: 6d57581659f7 ("perf record: Add support for limit perf output
> >> file size")
> >> Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> >> ---
> >>
> >> Changes since v2:
> >>   - Save data size written by threads to calculate the correct total
> >> data size.
> >>   - Update commit message.
> >>
> >> Changes since v1:
> >>   - Add variable check in record__bytes_written for code hardening.
> >>   - Save bytes_written separately to reduce one calculation.
> >>   - Remove rec->opts.tail_synthesize check.
> >>
> >>   tools/perf/builtin-record.c | 16 ++++++----------
> >>   1 file changed, 6 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> >> index 29dcd454b8e2..8374117e66f6 100644
> >> --- a/tools/perf/builtin-record.c
> >> +++ b/tools/perf/builtin-record.c
> >> @@ -154,6 +154,7 @@ struct record {
> >>       struct perf_tool    tool;
> >>       struct record_opts    opts;
> >>       u64            bytes_written;
> >> +    u64            thread_bytes_written;
> >>       struct perf_data    data;
> >>       struct auxtrace_record    *itr;
> >>       struct evlist    *evlist;
> >> @@ -226,14 +227,7 @@ static bool switch_output_time(struct record *rec)
> >>   static u64 record__bytes_written(struct record *rec)
> >>   {
> >> -    int t;
> >> -    u64 bytes_written = rec->bytes_written;
> >> -    struct record_thread *thread_data = rec->thread_data;
> >> -
> >> -    for (t = 0; t < rec->nr_threads; t++)
> >> -        bytes_written += thread_data[t].bytes_written;
> >> -
> >> -    return bytes_written;
> >> +    return rec->bytes_written + rec->thread_bytes_written;
> >>   }
> >>   static bool record__output_max_size_exceeded(struct record *rec)
> >> @@ -255,10 +249,12 @@ static int record__write(struct record *rec,
> >> struct mmap *map __maybe_unused,
> >>           return -1;
> >>       }
> >> -    if (map && map->file)
> >> +    if (map && map->file) {
> >>           thread->bytes_written += size;
> >> -    else
> >> +        rec->thread_bytes_written += size;
> >> +    } else {
> >>           rec->bytes_written += size;
> >> +    }
> >>       if (record__output_max_size_exceeded(rec) && !done) {
> >>           fprintf(stderr, "[ perf record: perf size limit reached (%"
> >> PRIu64 " KB),"
> >>
> >
> > .