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SubjectRe: [PATCH v2] perf record: Fix coredump with --overwrite and --max-size
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Hello,

On 2023/1/7 5:12, Namhyung Kim wrote:
> Hello,
>
> On Wed, Jan 4, 2023 at 8:09 PM Yang Jihong <yangjihong1@huawei.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@kernel.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@huawei.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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