Date:   Mon, 9 Jan 2023 10:46:48 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     Namhyung Kim <namhyung@...nel.org>
CC:     Arnaldo Carvalho de Melo <acme@...nel.org>, <peterz@...radead.org>,
        <mingo@...hat.com>, <mark.rutland@....com>,
        <alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
        <jiwei.sun@...driver.com>, <linux-perf-users@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] perf record: Fix coredump with --overwrite and
 --max-size

Hello,

On 2023/1/7 5:12, Namhyung Kim wrote:
> Hello,
> 
> On Wed, Jan 4, 2023 at 8:09 PM Yang Jihong <yangjihong1@...wei.com> wrote:
>>
>> Hello,
>>
>> On 2023/1/4 0:50, Namhyung Kim wrote:
>>> On Mon, Jan 2, 2023 at 8:20 AM Arnaldo Carvalho de Melo <acme@...nel.org> 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@...wei.com>
>>>>> ---
>>>>>
>>>>> 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.
>>>
>> I'm not sure here. Can you explain it more clearly, thanks :)
>> I can modify it accordingly.
>>
>> I think if thread_data == NULL, it is not thread data.
>> In this case, we just return rec->bytes_written.
> 
> It can be thread data but freed before tail synthesis, right?
> In that case, I think it needs to add bytes_written by threads
> to calculate the correct data size.
Em... In the __cmd_record function, record__stop_threads is called 
before record__free_thread_data, so if the thread has been freed, there 
will be no thread data.
I think it's okay to ignore the situation you mentioned above.

Thanks,
Yang

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