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

[Yang Jihong]

Hello,

On 2023/2/6 10:44, Namhyung Kim wrote:
> 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 for the review.

Thanks,
Yang.
> > 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),"
> > >
> > > .
>
> .