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

[Yang Jihong]

Hello,

Ping again, please take time to review, thanks.


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>
> > ---
> >
> > 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),"
>
> .