Re: [PATCH v2] perf record: Fix coredump with --overwrite and --max-size

[Namhyung Kim]

On Mon, Jan 2, 2023 at 8:20 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>
> Em Thu, Dec 29, 2022 at 12:47:28PM +0000, Yang Jihong escreveu:
> > 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 1M -a -- sleep 1
> >   [ perf record: Woken up 1 times to write data ]
> >   perf: Segmentation fault
> >   Obtained 1 stack frames.
> >   [0xc4c67f]
> >   Segmentation fault (core dumped)
> >
> > backtrace of the core file is as follows:
> >
> >   #0  0x0000000000417990 in process_locked_synthesized_event (tool=0x0, event=0x15, sample=0x1de0, machine=0xf8) at builtin-record.c:630
> >   #1  0x000000000057ee53 in perf_event__synthesize_threads (nr_threads_synthesize=21, mmap_data=<optimized out>, needs_mmap=<optimized out>, machine=0x17ad9b0, process=<optimized out>, tool=0x0) at util/synthetic-events.c:1950
> >   #2  __machine__synthesize_threads (nr_threads_synthesize=0, data_mmap=<optimized out>, needs_mmap=<optimized out>, process=<optimized out>, threads=0x8, target=0x8, tool=0x0, machine=0x17ad9b0) at util/synthetic-events.c:1936
> >   #3  machine__synthesize_threads (machine=0x17ad9b0, target=0x8, threads=0x8, needs_mmap=<optimized out>, data_mmap=<optimized out>, nr_threads_synthesize=0) at util/synthetic-events.c:1947
> >   #4  0x000000000040165d in record__synthesize (tail=<optimized out>, rec=0xbe2520 <record>) at builtin-record.c:2010
> >   #5  0x0000000000403989 in __cmd_record (argc=<optimized out>, argv=<optimized out>, rec=0xbe2520 <record>) at builtin-record.c:2810
> >   #6  0x00000000004196ba in record__init_thread_user_masks (rec=0xbe2520 <record>, cpus=0x17a65f0) at builtin-record.c:3837
> >   #7  record__init_thread_masks (rec=0xbe2520 <record>) at builtin-record.c:3938
> >   #8  cmd_record (argc=1, argv=0x7ffdd692dc60) at builtin-record.c:4241
> >   #9  0x00000000004b701d in pager_command_config (var=0x0, value=0x15 <error: Cannot access memory at address 0x15>, data=0x1de0) at perf.c:117
> >   #10 0x00000000004b732b in get_leaf_frame_caller_aarch64 (sample=0xfffffffb, thread=0x0, usr_idx=<optimized out>) at util/arm64-frame-pointer-unwind-support.c:56
> >   #11 0x0000000000406331 in execv_dashed_external (argv=0x7ffdd692d9e8) at perf.c:410
> >   #12 run_argv (argcp=<synthetic pointer>, argv=<synthetic pointer>) at perf.c:431
> >   #13 main (argc=<optimized out>, argv=0x7ffdd692d9e8) 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 only need to check the value of done first.
> > Also add variable check in record__bytes_written for code hardening,
> > and save bytes_written separately to reduce one calculation.
> >
> > Fixes: 6d57581659f7 ("perf record: Add support for limit perf output file size")
> > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> > ---
> >
> > 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.
>
> Namhyung, are you ok with this now?
>
> - Arnaldo
>
> >  tools/perf/builtin-record.c | 26 +++++++++++++++++---------
> >  1 file changed, 17 insertions(+), 9 deletions(-)
> >
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index 29dcd454b8e2..acba9e43e519 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -230,16 +230,29 @@ static u64 record__bytes_written(struct record *rec)
> >       u64 bytes_written = rec->bytes_written;
> >       struct record_thread *thread_data = rec->thread_data;
> >
> > +     if (thread_data == NULL)
> > +             return bytes_written;
> > +

Then it won't count bytes written by threads, right?
I think it needs to be saved somewhere.

Thanks,
Namhyung


> >       for (t = 0; t < rec->nr_threads; t++)
> >               bytes_written += thread_data[t].bytes_written;
> >
> >       return bytes_written;
> >  }
> >
> > -static bool record__output_max_size_exceeded(struct record *rec)
> > +static void record__check_output_max_size_exceeded(struct record *rec)
> >  {
> > -     return rec->output_max_size &&
> > -            (record__bytes_written(rec) >= rec->output_max_size);
> > +     u64 bytes_written;
> > +
> > +     if (rec->output_max_size == 0 || done)
> > +             return;
> > +
> > +     bytes_written = record__bytes_written(rec);
> > +     if (bytes_written >= rec->output_max_size) {
> > +             fprintf(stderr, "[ perf record: perf size limit reached (%" PRIu64 " KB),"
> > +                     " stopping session ]\n", bytes_written >> 10);
> > +
> > +             done = 1;
> > +     }
> >  }
> >
> >  static int record__write(struct record *rec, struct mmap *map __maybe_unused,
> > @@ -260,12 +273,7 @@ static int record__write(struct record *rec, struct mmap *map __maybe_unused,
> >       else
> >               rec->bytes_written += size;
> >
> > -     if (record__output_max_size_exceeded(rec) && !done) {
> > -             fprintf(stderr, "[ perf record: perf size limit reached (%" PRIu64 " KB),"
> > -                             " stopping session ]\n",
> > -                             record__bytes_written(rec) >> 10);
> > -             done = 1;
> > -     }
> > +     record__check_output_max_size_exceeded(rec);
> >
> >       if (switch_output_size(rec))
> >               trigger_hit(&switch_output_trigger);
> > --
> > 2.30.GIT
>
> --
>
> - Arnaldo